diff --git a/cmd/zdb/zdb.c b/cmd/zdb/zdb.c
index 55a6c4fa1bb1..21f8ea87c446 100644
--- a/cmd/zdb/zdb.c
+++ b/cmd/zdb/zdb.c
@@ -2165,6 +2165,13 @@ dump_uberblock(uberblock_t *ub, const char *header, const char *footer)
 	(void) printf("\tguid_sum = %llu\n", (u_longlong_t)ub->ub_guid_sum);
 	(void) printf("\ttimestamp = %llu UTC = %s",
 	    (u_longlong_t)ub->ub_timestamp, asctime(localtime(&timestamp)));
+
+	(void) printf("\tmmp_magic = %016llx\n",
+	    (u_longlong_t)ub->ub_mmp_magic);
+	if (ub->ub_mmp_magic == MMP_MAGIC)
+		(void) printf("\tmmp_delay = %0llu\n",
+		    (u_longlong_t)ub->ub_mmp_delay);
+
 	if (dump_opt['u'] >= 4) {
 		char blkbuf[BP_SPRINTF_LEN];
 		snprintf_blkptr(blkbuf, sizeof (blkbuf), &ub->ub_rootbp);
@@ -2529,6 +2536,11 @@ dump_label_uberblocks(label_t *label, uint64_t ashift, int label_num)
 		if ((dump_opt['u'] < 3) && (first_label(rec) != label_num))
 			continue;
 
+		if ((dump_opt['u'] < 4) &&
+		    (ub->ub_mmp_magic == MMP_MAGIC) && ub->ub_mmp_delay &&
+		    (i >= VDEV_UBERBLOCK_COUNT(&vd) - MMP_BLOCKS_PER_LABEL))
+			continue;
+
 		print_label_header(label, label_num);
 		(void) snprintf(header, ZDB_MAX_UB_HEADER_SIZE,
 		    "    Uberblock[%d]\n", i);
@@ -4125,89 +4137,6 @@ zdb_embedded_block(char *thing)
 	zdb_dump_block_raw(buf, BPE_GET_LSIZE(&bp), 0);
 }
 
-static boolean_t
-pool_match(nvlist_t *cfg, char *tgt)
-{
-	uint64_t v, guid = strtoull(tgt, NULL, 0);
-	char *s;
-
-	if (guid != 0) {
-		if (nvlist_lookup_uint64(cfg, ZPOOL_CONFIG_POOL_GUID, &v) == 0)
-			return (v == guid);
-	} else {
-		if (nvlist_lookup_string(cfg, ZPOOL_CONFIG_POOL_NAME, &s) == 0)
-			return (strcmp(s, tgt) == 0);
-	}
-	return (B_FALSE);
-}
-
-static char *
-find_zpool(char **target, nvlist_t **configp, int dirc, char **dirv)
-{
-	nvlist_t *pools;
-	nvlist_t *match = NULL;
-	char *name = NULL;
-	char *sepp = NULL;
-	char sep = '\0';
-	int count = 0;
-	importargs_t args = { 0 };
-
-	args.paths = dirc;
-	args.path = dirv;
-	args.can_be_active = B_TRUE;
-
-	if ((sepp = strpbrk(*target, "/@")) != NULL) {
-		sep = *sepp;
-		*sepp = '\0';
-	}
-
-	pools = zpool_search_import(g_zfs, &args);
-
-	if (pools != NULL) {
-		nvpair_t *elem = NULL;
-		while ((elem = nvlist_next_nvpair(pools, elem)) != NULL) {
-			verify(nvpair_value_nvlist(elem, configp) == 0);
-			if (pool_match(*configp, *target)) {
-				count++;
-				if (match != NULL) {
-					/* print previously found config */
-					if (name != NULL) {
-						(void) printf("%s\n", name);
-						dump_nvlist(match, 8);
-						name = NULL;
-					}
-					(void) printf("%s\n",
-					    nvpair_name(elem));
-					dump_nvlist(*configp, 8);
-				} else {
-					match = *configp;
-					name = nvpair_name(elem);
-				}
-			}
-		}
-	}
-	if (count > 1)
-		(void) fatal("\tMatched %d pools - use pool GUID "
-		    "instead of pool name or \n"
-		    "\tpool name part of a dataset name to select pool", count);
-
-	if (sepp)
-		*sepp = sep;
-	/*
-	 * If pool GUID was specified for pool id, replace it with pool name
-	 */
-	if (name && (strstr(*target, name) != *target)) {
-		int sz = 1 + strlen(name) + ((sepp) ? strlen(sepp) : 0);
-
-		*target = umem_alloc(sz, UMEM_NOFAIL);
-		(void) snprintf(*target, sz, "%s%s", name, sepp ? sepp : "");
-	}
-
-	*configp = name ? match : NULL;
-
-	return (name);
-}
-
 int
 main(int argc, char **argv)
 {
@@ -4424,21 +4353,31 @@ main(int argc, char **argv)
 	target = argv[0];
 
 	if (dump_opt['e']) {
+		importargs_t args = { 0 };
 		nvlist_t *cfg = NULL;
-		char *name = find_zpool(&target, &cfg, nsearch, searchdirs);
 
-		error = ENOENT;
-		if (name) {
-			if (dump_opt['C'] > 1) {
-				(void) printf("\nConfiguration for import:\n");
-				dump_nvlist(cfg, 8);
-			}
+		args.paths = nsearch;
+		args.path = searchdirs;
+		args.can_be_active = B_TRUE;
+
+		error = zpool_tryimport(g_zfs, target, &cfg, &args);
+		if (error == 0) {
 			if (nvlist_add_nvlist(cfg,
 			    ZPOOL_REWIND_POLICY, policy) != 0) {
 				fatal("can't open '%s': %s",
 				    target, strerror(ENOMEM));
 			}
-			error = spa_import(name, cfg, NULL, flags);
+
+			/*
+			 * Disable the activity check to allow examination of
+			 * active pools.
+			 */
+			if (dump_opt['C'] > 1) {
+				(void) printf("\nConfiguration for import:\n");
+				dump_nvlist(cfg, 8);
+			}
+			error = spa_import(target, cfg, NULL,
+			    flags | ZFS_IMPORT_SKIP_MMP);
 		}
 	}
 
@@ -4453,6 +4392,16 @@ main(int argc, char **argv)
 
 	if (error == 0) {
 		if (target_is_spa || dump_opt['R']) {
+			/*
+			 * Disable the activity check to allow examination of
+			 * active pools.
+			 */
+			mutex_enter(&spa_namespace_lock);
+			if ((spa = spa_lookup(target)) != NULL) {
+				spa->spa_import_flags |= ZFS_IMPORT_SKIP_MMP;
+			}
+			mutex_exit(&spa_namespace_lock);
+
 			error = spa_open_rewind(target, &spa, FTAG, policy,
 			    NULL);
 			if (error) {
diff --git a/cmd/zhack/zhack.c b/cmd/zhack/zhack.c
index e76945141afb..cc414dae1565 100644
--- a/cmd/zhack/zhack.c
+++ b/cmd/zhack/zhack.c
@@ -121,16 +121,11 @@ space_delta_cb(dmu_object_type_t bonustype, void *data,
  * Target is the dataset whose pool we want to open.
  */
 static void
-import_pool(const char *target, boolean_t readonly)
+zhack_import(char *target, boolean_t readonly)
 {
 	nvlist_t *config;
-	nvlist_t *pools;
-	int error;
-	char *sepp;
-	spa_t *spa;
-	nvpair_t *elem;
 	nvlist_t *props;
-	char *name;
+	int error;
 
 	kernel_init(readonly ? FREAD : (FREAD | FWRITE));
 	g_zfs = libzfs_init();
@@ -139,43 +134,14 @@ import_pool(const char *target, boolean_t readonly)
 	dmu_objset_register_type(DMU_OST_ZFS, space_delta_cb);
 
 	g_readonly = readonly;
-
-	/*
-	 * If we only want readonly access, it's OK if we find
-	 * a potentially-active (ie, imported into the kernel) pool from the
-	 * default cachefile.
-	 */
-	if (readonly && spa_open(target, &spa, FTAG) == 0) {
-		spa_close(spa, FTAG);
-		return;
-	}
-
 	g_importargs.unique = B_TRUE;
 	g_importargs.can_be_active = readonly;
 	g_pool = strdup(target);
-	if ((sepp = strpbrk(g_pool, "/@")) != NULL)
-		*sepp = '\0';
-	g_importargs.poolname = g_pool;
-	pools = zpool_search_import(g_zfs, &g_importargs);
-
-	if (nvlist_empty(pools)) {
-		if (!g_importargs.can_be_active) {
-			g_importargs.can_be_active = B_TRUE;
-			if (zpool_search_import(g_zfs, &g_importargs) != NULL ||
-			    spa_open(target, &spa, FTAG) == 0) {
-				fatal(spa, FTAG, "cannot import '%s': pool is "
-				    "active; run " "\"zpool export %s\" "
-				    "first\n", g_pool, g_pool);
-			}
-		}
 
-		fatal(NULL, FTAG, "cannot import '%s': no such pool "
-		    "available\n", g_pool);
-	}
-
-	elem = nvlist_next_nvpair(pools, NULL);
-	name = nvpair_name(elem);
-	VERIFY(nvpair_value_nvlist(elem, &config) == 0);
+	error = zpool_tryimport(g_zfs, target, &config, &g_importargs);
+	if (error)
+		fatal(NULL, FTAG, "cannot import '%s': %s", target,
+		    libzfs_error_description(g_zfs));
 
 	props = NULL;
 	if (readonly) {
@@ -185,22 +151,22 @@ import_pool(const char *target, boolean_t readonly)
 	}
 
 	zfeature_checks_disable = B_TRUE;
-	error = spa_import(name, config, props, ZFS_IMPORT_NORMAL);
+	error = spa_import(target, config, props, ZFS_IMPORT_NORMAL);
 	zfeature_checks_disable = B_FALSE;
 	if (error == EEXIST)
 		error = 0;
 
 	if (error)
-		fatal(NULL, FTAG, "can't import '%s': %s", name,
+		fatal(NULL, FTAG, "can't import '%s': %s", target,
 		    strerror(error));
 }
 
 static void
-zhack_spa_open(const char *target, boolean_t readonly, void *tag, spa_t **spa)
+zhack_spa_open(char *target, boolean_t readonly, void *tag, spa_t **spa)
 {
 	int err;
 
-	import_pool(target, readonly);
+	zhack_import(target, readonly);
 
 	zfeature_checks_disable = B_TRUE;
 	err = spa_open(target, spa, tag);
diff --git a/cmd/zpool/zpool_main.c b/cmd/zpool/zpool_main.c
index 14181b083755..052b429cc722 100644
--- a/cmd/zpool/zpool_main.c
+++ b/cmd/zpool/zpool_main.c
@@ -1743,6 +1743,9 @@ print_status_config(zpool_handle_t *zhp, status_cbdata_t *cb, const char *name,
 			(void) printf(gettext("split into new pool"));
 			break;
 
+		case VDEV_AUX_ACTIVE:
+			(void) printf(gettext("currently in use"));
+
 		default:
 			(void) printf(gettext("corrupted data"));
 			break;
@@ -1838,6 +1841,10 @@ print_import_config(status_cbdata_t *cb, const char *name, nvlist_t *nv,
 			(void) printf(gettext("too many errors"));
 			break;
 
+		case VDEV_AUX_ACTIVE:
+			(void) printf(gettext("currently in use"));
+			break;
+
 		default:
 			(void) printf(gettext("corrupted data"));
 			break;
@@ -1935,8 +1942,10 @@ show_import(nvlist_t *config)
 	vdev_stat_t *vs;
 	char *name;
 	uint64_t guid;
+	uint64_t hostid = 0;
 	char *msgid;
-	nvlist_t *nvroot;
+	char *hostname = "unknown";
+	nvlist_t *nvroot, *nvinfo;
 	zpool_status_t reason;
 	zpool_errata_t errata;
 	const char *health;
@@ -2024,6 +2033,17 @@ show_import(nvlist_t *config)
 		zpool_print_unsup_feat(config);
 		break;
 
+	case ZPOOL_STATUS_HOSTID_ACTIVE:
+		(void) printf(gettext(" status: The pool is currently "
+		    "imported by another system.\n"));
+		break;
+
+	case ZPOOL_STATUS_HOSTID_REQUIRED:
+		(void) printf(gettext(" status: The pool has the "
+		    "multihost property on.  It cannot\n\tbe safely imported "
+		    "when the system hostid is not set.\n"));
+		break;
+
 	case ZPOOL_STATUS_HOSTID_MISMATCH:
 		(void) printf(gettext(" status: The pool was last accessed by "
 		    "another system.\n"));
@@ -2137,6 +2157,27 @@ show_import(nvlist_t *config)
 			    "imported. Attach the missing\n\tdevices and try "
 			    "again.\n"));
 			break;
+		case ZPOOL_STATUS_HOSTID_ACTIVE:
+			VERIFY0(nvlist_lookup_nvlist(config,
+			    ZPOOL_CONFIG_LOAD_INFO, &nvinfo));
+
+			if (nvlist_exists(nvinfo, ZPOOL_CONFIG_MMP_HOSTNAME))
+				hostname = fnvlist_lookup_string(nvinfo,
+				    ZPOOL_CONFIG_MMP_HOSTNAME);
+
+			if (nvlist_exists(nvinfo, ZPOOL_CONFIG_MMP_HOSTID))
+				hostid = fnvlist_lookup_uint64(nvinfo,
+				    ZPOOL_CONFIG_MMP_HOSTID);
+
+			(void) printf(gettext(" action: The pool must be "
+			    "exported from %s (hostid=%lx)\n\tbefore it "
+			    "can be safely imported.\n"), hostname,
+			    (unsigned long) hostid);
+			break;
+		case ZPOOL_STATUS_HOSTID_REQUIRED:
+			(void) printf(gettext(" action: Set a unique system "
+			    "hostid with the genhostid(1) command.\n"));
+			break;
 		default:
 			(void) printf(gettext(" action: The pool cannot be "
 			    "imported due to damaged devices or data.\n"));
@@ -2184,6 +2225,31 @@ show_import(nvlist_t *config)
 	}
 }
 
+static boolean_t
+zfs_force_import_required(nvlist_t *config)
+{
+	uint64_t state;
+	uint64_t hostid = 0;
+	nvlist_t *nvinfo;
+
+	state = fnvlist_lookup_uint64(config, ZPOOL_CONFIG_POOL_STATE);
+	(void) nvlist_lookup_uint64(config, ZPOOL_CONFIG_HOSTID, &hostid);
+
+	if (state != POOL_STATE_EXPORTED && hostid != get_system_hostid())
+		return (B_TRUE);
+
+	nvinfo = fnvlist_lookup_nvlist(config, ZPOOL_CONFIG_LOAD_INFO);
+	if (nvlist_exists(nvinfo, ZPOOL_CONFIG_MMP_STATE)) {
+		mmp_state_t mmp_state = fnvlist_lookup_uint64(nvinfo,
+		    ZPOOL_CONFIG_MMP_STATE);
+
+		if (mmp_state != MMP_STATE_INACTIVE)
+			return (B_TRUE);
+	}
+
+	return (B_FALSE);
+}
+
 /*
  * Perform the import for the given configuration.  This passes the heavy
  * lifting off to zpool_import_props(), and then mounts the datasets contained
@@ -2198,45 +2264,72 @@ do_import(nvlist_t *config, const char *newname, const char *mntopts,
 	uint64_t state;
 	uint64_t version;
 
-	verify(nvlist_lookup_string(config, ZPOOL_CONFIG_POOL_NAME,
-	    &name) == 0);
+	name = fnvlist_lookup_string(config, ZPOOL_CONFIG_POOL_NAME);
+	state = fnvlist_lookup_uint64(config, ZPOOL_CONFIG_POOL_STATE);
+	version = fnvlist_lookup_uint64(config, ZPOOL_CONFIG_VERSION);
 
-	verify(nvlist_lookup_uint64(config,
-	    ZPOOL_CONFIG_POOL_STATE, &state) == 0);
-	verify(nvlist_lookup_uint64(config,
-	    ZPOOL_CONFIG_VERSION, &version) == 0);
 	if (!SPA_VERSION_IS_SUPPORTED(version)) {
 		(void) fprintf(stderr, gettext("cannot import '%s': pool "
 		    "is formatted using an unsupported ZFS version\n"), name);
 		return (1);
-	} else if (state != POOL_STATE_EXPORTED &&
+	} else if (zfs_force_import_required(config) &&
 	    !(flags & ZFS_IMPORT_ANY_HOST)) {
-		uint64_t hostid = 0;
-		unsigned long system_hostid = get_system_hostid();
+		mmp_state_t mmp_state = MMP_STATE_INACTIVE;
+		nvlist_t *nvinfo;
 
-		(void) nvlist_lookup_uint64(config, ZPOOL_CONFIG_HOSTID,
-		    &hostid);
+		nvinfo = fnvlist_lookup_nvlist(config, ZPOOL_CONFIG_LOAD_INFO);
+		if (nvlist_exists(nvinfo, ZPOOL_CONFIG_MMP_STATE))
+			mmp_state = fnvlist_lookup_uint64(nvinfo,
+			    ZPOOL_CONFIG_MMP_STATE);
 
-		if (hostid != 0 && (unsigned long)hostid != system_hostid) {
-			char *hostname;
-			uint64_t timestamp;
-			time_t t;
+		if (mmp_state == MMP_STATE_ACTIVE) {
+			char *hostname = "<unknown>";
+			uint64_t hostid = 0;
 
-			verify(nvlist_lookup_string(config,
-			    ZPOOL_CONFIG_HOSTNAME, &hostname) == 0);
-			verify(nvlist_lookup_uint64(config,
-			    ZPOOL_CONFIG_TIMESTAMP, &timestamp) == 0);
-			t = timestamp;
-			(void) fprintf(stderr, gettext("cannot import "
-			    "'%s': pool may be in use from other "
-			    "system, it was last accessed by %s "
-			    "(hostid: 0x%lx) on %s"), name, hostname,
-			    (unsigned long)hostid,
-			    asctime(localtime(&t)));
-			(void) fprintf(stderr, gettext("use '-f' to "
-			    "import anyway\n"));
-			return (1);
+			if (nvlist_exists(nvinfo, ZPOOL_CONFIG_MMP_HOSTNAME))
+				hostname = fnvlist_lookup_string(nvinfo,
+				    ZPOOL_CONFIG_MMP_HOSTNAME);
+
+			if (nvlist_exists(nvinfo, ZPOOL_CONFIG_MMP_HOSTID))
+				hostid = fnvlist_lookup_uint64(nvinfo,
+				    ZPOOL_CONFIG_MMP_HOSTID);
+
+			(void) fprintf(stderr, gettext("cannot import '%s': "
+			    "pool is imported on %s (hostid: "
+			    "0x%lx)\nExport the pool on the other system, "
+			    "then run 'zpool import'.\n"),
+			    name, hostname, (unsigned long) hostid);
+		} else if (mmp_state == MMP_STATE_NO_HOSTID) {
+			(void) fprintf(stderr, gettext("Cannot import '%s': "
+			    "pool has the multihost property on and the\n"
+			    "system's hostid is not set. Set a unique hostid "
+			    "with the genhostid(1) command.\n"), name);
+		} else {
+			char *hostname = "<unknown>";
+			uint64_t timestamp = 0;
+			uint64_t hostid = 0;
+
+			if (nvlist_exists(config, ZPOOL_CONFIG_HOSTNAME))
+				hostname = fnvlist_lookup_string(config,
+				    ZPOOL_CONFIG_HOSTNAME);
+
+			if (nvlist_exists(config, ZPOOL_CONFIG_TIMESTAMP))
+				timestamp = fnvlist_lookup_uint64(config,
+				    ZPOOL_CONFIG_TIMESTAMP);
+
+			if (nvlist_exists(config, ZPOOL_CONFIG_HOSTID))
+				hostid = fnvlist_lookup_uint64(config,
+				    ZPOOL_CONFIG_HOSTID);
+
+			(void) fprintf(stderr, gettext("cannot import '%s': "
+			    "pool was previously in use from another system.\n"
+			    "Last accessed by %s (hostid=%lx) at %s"
+			    "The pool can be imported, use 'zpool import -f' "
+			    "to import the pool.\n"), name, hostname,
+			    (unsigned long)hostid, ctime((time_t *)&timestamp));
 		}
+
+		return (1);
 	}
 
 	if (zpool_import_props(g_zfs, config, newname, props, flags) != 0)
diff --git a/cmd/ztest/ztest.c b/cmd/ztest/ztest.c
index d698628ded43..b4cedbdbaf66 100644
--- a/cmd/ztest/ztest.c
+++ b/cmd/ztest/ztest.c
@@ -126,6 +126,7 @@
 #include <sys/fs/zfs.h>
 #include <zfs_fletcher.h>
 #include <libnvpair.h>
+#include <libzfs.h>
 #ifdef __GLIBC__
 #include <execinfo.h> /* for backtrace() */
 #endif
@@ -166,6 +167,7 @@ typedef struct ztest_shared_opts {
 	uint64_t zo_time;
 	uint64_t zo_maxloops;
 	uint64_t zo_metaslab_gang_bang;
+	int zo_mmp_test;
 } ztest_shared_opts_t;
 
 static const ztest_shared_opts_t ztest_opts_defaults = {
@@ -184,6 +186,7 @@ static const ztest_shared_opts_t ztest_opts_defaults = {
 	.zo_passtime = 60,		/* 60 seconds */
 	.zo_killrate = 70,		/* 70% kill rate */
 	.zo_verbose = 0,
+	.zo_mmp_test = 0,
 	.zo_init = 1,
 	.zo_time = 300,			/* 5 minutes */
 	.zo_maxloops = 50,		/* max loops during spa_freeze() */
@@ -623,6 +626,7 @@ usage(boolean_t requested)
 	    "\t[-k kill_percentage (default: %llu%%)]\n"
 	    "\t[-p pool_name (default: %s)]\n"
 	    "\t[-f dir (default: %s)] file directory for vdev files\n"
+	    "\t[-M] Multi-host simulate pool imported on remote host\n"
 	    "\t[-V] verbose (use multiple times for ever more blather)\n"
 	    "\t[-E] use existing pool instead of creating new one\n"
 	    "\t[-T time (default: %llu sec)] total run time\n"
@@ -666,7 +670,7 @@ process_options(int argc, char **argv)
 	bcopy(&ztest_opts_defaults, zo, sizeof (*zo));
 
 	while ((opt = getopt(argc, argv,
-	    "v:s:a:m:r:R:d:t:g:i:k:p:f:VET:P:hF:B:o:")) != EOF) {
+	    "v:s:a:m:r:R:d:t:g:i:k:p:f:MVET:P:hF:B:o:")) != EOF) {
 		value = 0;
 		switch (opt) {
 		case 'v':
@@ -736,6 +740,9 @@ process_options(int argc, char **argv)
 				free(path);
 			}
 			break;
+		case 'M':
+			zo->zo_mmp_test = 1;
+			break;
 		case 'V':
 			zo->zo_verbose++;
 			break;
@@ -2619,6 +2626,9 @@ ztest_spa_create_destroy(ztest_ds_t *zd, uint64_t id)
 	spa_t *spa;
 	nvlist_t *nvroot;
 
+	if (zo->zo_mmp_test)
+		return;
+
 	/*
 	 * Attempt to create using a bad file.
 	 */
@@ -2660,6 +2670,9 @@ ztest_spa_upgrade(ztest_ds_t *zd, uint64_t id)
 	nvlist_t *nvroot, *props;
 	char *name;
 
+	if (ztest_opts.zo_mmp_test)
+		return;
+
 	mutex_enter(&ztest_vdev_lock);
 	name = kmem_asprintf("%s_upgrade", ztest_opts.zo_pool);
 
@@ -2773,6 +2786,9 @@ ztest_vdev_add_remove(ztest_ds_t *zd, uint64_t id)
 	nvlist_t *nvroot;
 	int error;
 
+	if (ztest_opts.zo_mmp_test)
+		return;
+
 	mutex_enter(&ztest_vdev_lock);
 	leaves = MAX(zs->zs_mirrors + zs->zs_splits, 1) * ztest_opts.zo_raidz;
 
@@ -2844,6 +2860,9 @@ ztest_vdev_aux_add_remove(ztest_ds_t *zd, uint64_t id)
 	uint64_t guid = 0;
 	int error;
 
+	if (ztest_opts.zo_mmp_test)
+		return;
+
 	path = umem_alloc(MAXPATHLEN, UMEM_NOFAIL);
 
 	if (ztest_random(2) == 0) {
@@ -2929,6 +2948,9 @@ ztest_split_pool(ztest_ds_t *zd, uint64_t id)
 	uint_t c, children, schildren = 0, lastlogid = 0;
 	int error = 0;
 
+	if (ztest_opts.zo_mmp_test)
+		return;
+
 	mutex_enter(&ztest_vdev_lock);
 
 	/* ensure we have a useable config; mirrors of raidz aren't supported */
@@ -3036,6 +3058,9 @@ ztest_vdev_attach_detach(ztest_ds_t *zd, uint64_t id)
 	int oldvd_is_log;
 	int error, expected_error;
 
+	if (ztest_opts.zo_mmp_test)
+		return;
+
 	oldpath = umem_alloc(MAXPATHLEN, UMEM_NOFAIL);
 	newpath = umem_alloc(MAXPATHLEN, UMEM_NOFAIL);
 
@@ -5624,6 +5649,9 @@ ztest_spa_rename(ztest_ds_t *zd, uint64_t id)
 	char *oldname, *newname;
 	spa_t *spa;
 
+	if (ztest_opts.zo_mmp_test)
+		return;
+
 	(void) rw_wrlock(&ztest_name_lock);
 
 	oldname = ztest_opts.zo_pool;
@@ -6414,7 +6442,7 @@ ztest_run(ztest_shared_t *zs)
 	 * Verify that we can export the pool and reimport it under a
 	 * different name.
 	 */
-	if (ztest_random(2) == 0) {
+	if ((ztest_random(2) == 0) && !ztest_opts.zo_mmp_test) {
 		char name[ZFS_MAX_DATASET_NAME_LEN];
 		(void) snprintf(name, sizeof (name), "%s_import",
 		    ztest_opts.zo_pool);
@@ -6561,6 +6589,56 @@ make_random_props(void)
 	return (props);
 }
 
+/*
+ * Import a storage pool with the given name.
+ */
+static void
+ztest_import(ztest_shared_t *zs)
+{
+	libzfs_handle_t *hdl;
+	importargs_t args = { 0 };
+	spa_t *spa;
+	nvlist_t *cfg = NULL;
+	int nsearch = 1;
+	char *searchdirs[nsearch];
+	char *name = ztest_opts.zo_pool;
+	int flags = ZFS_IMPORT_MISSING_LOG;
+	int error;
+
+	mutex_init(&ztest_vdev_lock, NULL, MUTEX_DEFAULT, NULL);
+	VERIFY(rwlock_init(&ztest_name_lock, USYNC_THREAD, NULL) == 0);
+
+	kernel_init(FREAD | FWRITE);
+	hdl = libzfs_init();
+
+	searchdirs[0] = ztest_opts.zo_dir;
+	args.paths = nsearch;
+	args.path = searchdirs;
+	args.can_be_active = B_FALSE;
+
+	error = zpool_tryimport(hdl, name, &cfg, &args);
+	if (error)
+		(void) fatal(0, "No pools found\n");
+
+	VERIFY0(spa_import(name, cfg, NULL, flags));
+	VERIFY0(spa_open(name, &spa, FTAG));
+	zs->zs_metaslab_sz =
+	    1ULL << spa->spa_root_vdev->vdev_child[0]->vdev_ms_shift;
+	spa_close(spa, FTAG);
+
+	libzfs_fini(hdl);
+	kernel_fini();
+
+	if (!ztest_opts.zo_mmp_test) {
+		ztest_run_zdb(ztest_opts.zo_pool);
+		ztest_freeze();
+		ztest_run_zdb(ztest_opts.zo_pool);
+	}
+
+	(void) rwlock_destroy(&ztest_name_lock);
+	mutex_destroy(&ztest_vdev_lock);
+}
+
 /*
  * Create a storage pool with the given name and initial vdev size.
  * Then test spa_freeze() functionality.
@@ -6605,11 +6683,11 @@ ztest_init(ztest_shared_t *zs)
 
 	kernel_fini();
 
-	ztest_run_zdb(ztest_opts.zo_pool);
-
-	ztest_freeze();
-
-	ztest_run_zdb(ztest_opts.zo_pool);
+	if (!ztest_opts.zo_mmp_test) {
+		ztest_run_zdb(ztest_opts.zo_pool);
+		ztest_freeze();
+		ztest_run_zdb(ztest_opts.zo_pool);
+	}
 
 	(void) rwlock_destroy(&ztest_name_lock);
 	mutex_destroy(&ztest_vdev_lock);
@@ -6769,13 +6847,19 @@ ztest_run_init(void)
 
 	ztest_shared_t *zs = ztest_shared;
 
-	ASSERT(ztest_opts.zo_init != 0);
-
 	/*
 	 * Blow away any existing copy of zpool.cache
 	 */
 	(void) remove(spa_config_path);
 
+	if (ztest_opts.zo_init == 0) {
+		if (ztest_opts.zo_verbose >= 1)
+			(void) printf("Importing pool %s\n",
+			    ztest_opts.zo_pool);
+		ztest_import(zs);
+		return;
+	}
+
 	/*
 	 * Create and initialize our storage pool.
 	 */
@@ -7002,7 +7086,8 @@ main(int argc, char **argv)
 		}
 		kernel_fini();
 
-		ztest_run_zdb(ztest_opts.zo_pool);
+		if (!ztest_opts.zo_mmp_test)
+			ztest_run_zdb(ztest_opts.zo_pool);
 	}
 
 	if (ztest_opts.zo_verbose >= 1) {
diff --git a/configure.ac b/configure.ac
index c52d72e3dd84..514fcd98e1a9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -253,6 +253,7 @@ AC_CONFIG_FILES([
 	tests/zfs-tests/tests/functional/libzfs/Makefile
 	tests/zfs-tests/tests/functional/migration/Makefile
 	tests/zfs-tests/tests/functional/mmap/Makefile
+	tests/zfs-tests/tests/functional/mmp/Makefile
 	tests/zfs-tests/tests/functional/mount/Makefile
 	tests/zfs-tests/tests/functional/mv_files/Makefile
 	tests/zfs-tests/tests/functional/nestedfs/Makefile
diff --git a/include/libzfs.h b/include/libzfs.h
index c03ff5710ded..147589bbfdad 100644
--- a/include/libzfs.h
+++ b/include/libzfs.h
@@ -148,6 +148,7 @@ typedef enum zfs_error {
 	EZFS_DIFFDATA,		/* bad zfs diff data */
 	EZFS_POOLREADONLY,	/* pool is in read-only mode */
 	EZFS_SCRUB_PAUSED,	/* scrub currently paused */
+	EZFS_ACTIVE_POOL,	/* pool is imported on a different system */
 	EZFS_UNKNOWN
 } zfs_error_t;
 
@@ -326,6 +327,8 @@ typedef enum {
 	ZPOOL_STATUS_FAILING_DEV,	/* device experiencing errors */
 	ZPOOL_STATUS_VERSION_NEWER,	/* newer on-disk version */
 	ZPOOL_STATUS_HOSTID_MISMATCH,	/* last accessed by another system */
+	ZPOOL_STATUS_HOSTID_ACTIVE,	/* currently active on another system */
+	ZPOOL_STATUS_HOSTID_REQUIRED,	/* multihost=on and hostid=0 */
 	ZPOOL_STATUS_IO_FAILURE_WAIT,	/* failed I/O, failmode 'wait' */
 	ZPOOL_STATUS_IO_FAILURE_CONTINUE, /* failed I/O, failmode 'continue' */
 	ZPOOL_STATUS_BAD_LOG,		/* cannot read log chain(s) */
@@ -408,6 +411,8 @@ typedef struct importargs {
 } importargs_t;
 
 extern nvlist_t *zpool_search_import(libzfs_handle_t *, importargs_t *);
+extern int zpool_tryimport(libzfs_handle_t *hdl, char *target,
+    nvlist_t **configp, importargs_t *args);
 
 /* legacy pool search routines */
 extern nvlist_t *zpool_find_import(libzfs_handle_t *, int, char **);
diff --git a/include/libzfs_impl.h b/include/libzfs_impl.h
index 75a7bc2490fb..2efd85e31a75 100644
--- a/include/libzfs_impl.h
+++ b/include/libzfs_impl.h
@@ -131,7 +131,7 @@ typedef enum {
 	SHARED_SMB = 0x4
 } zfs_share_type_t;
 
-#define	CONFIG_BUF_MINSIZE	65536
+#define	CONFIG_BUF_MINSIZE	262144
 
 int zfs_error(libzfs_handle_t *, int, const char *);
 int zfs_error_fmt(libzfs_handle_t *, int, const char *, ...);
diff --git a/include/sys/Makefile.am b/include/sys/Makefile.am
index 956643801c66..be606b8c6060 100644
--- a/include/sys/Makefile.am
+++ b/include/sys/Makefile.am
@@ -36,6 +36,7 @@ COMMON_H = \
 	$(top_srcdir)/include/sys/efi_partition.h \
 	$(top_srcdir)/include/sys/metaslab.h \
 	$(top_srcdir)/include/sys/metaslab_impl.h \
+	$(top_srcdir)/include/sys/mmp.h \
 	$(top_srcdir)/include/sys/mntent.h \
 	$(top_srcdir)/include/sys/multilist.h \
 	$(top_srcdir)/include/sys/nvpair.h \
diff --git a/include/sys/dsl_pool.h b/include/sys/dsl_pool.h
index 674dd25b56d4..d2dabda6df19 100644
--- a/include/sys/dsl_pool.h
+++ b/include/sys/dsl_pool.h
@@ -38,6 +38,7 @@
 #include <sys/bpobj.h>
 #include <sys/bptree.h>
 #include <sys/rrwlock.h>
+#include <sys/mmp.h>
 
 #ifdef	__cplusplus
 extern "C" {
diff --git a/include/sys/fs/zfs.h b/include/sys/fs/zfs.h
index 9fbcfbef3b25..13b25a695639 100644
--- a/include/sys/fs/zfs.h
+++ b/include/sys/fs/zfs.h
@@ -223,6 +223,7 @@ typedef enum {
 	ZPOOL_PROP_MAXBLOCKSIZE,
 	ZPOOL_PROP_TNAME,
 	ZPOOL_PROP_MAXDNODESIZE,
+	ZPOOL_PROP_MULTIHOST,
 	ZPOOL_NUM_PROPS
 } zpool_prop_t;
 
@@ -651,6 +652,11 @@ typedef struct zpool_rewind_policy {
 #define	ZPOOL_CONFIG_VDEV_TOP_ZAP	"com.delphix:vdev_zap_top"
 #define	ZPOOL_CONFIG_VDEV_LEAF_ZAP	"com.delphix:vdev_zap_leaf"
 #define	ZPOOL_CONFIG_HAS_PER_VDEV_ZAPS	"com.delphix:has_per_vdev_zaps"
+#define	ZPOOL_CONFIG_MMP_STATE		"mmp_state"	/* not stored on disk */
+#define	ZPOOL_CONFIG_MMP_TXG		"mmp_txg"	/* not stored on disk */
+#define	ZPOOL_CONFIG_MMP_HOSTNAME	"mmp_hostname"	/* not stored on disk */
+#define	ZPOOL_CONFIG_MMP_HOSTID		"mmp_hostid"	/* not stored on disk */
+
 /*
  * The persistent vdev state is stored as separate values rather than a single
  * 'vdev_state' entry.  This is because a device can be in multiple states, such
@@ -744,7 +750,8 @@ typedef enum vdev_aux {
 	VDEV_AUX_EXTERNAL,	/* external diagnosis or forced fault	*/
 	VDEV_AUX_SPLIT_POOL,	/* vdev was split off into another pool	*/
 	VDEV_AUX_BAD_ASHIFT,	/* vdev ashift is invalid		*/
-	VDEV_AUX_EXTERNAL_PERSIST	/* persistent forced fault	*/
+	VDEV_AUX_EXTERNAL_PERSIST,	/* persistent forced fault	*/
+	VDEV_AUX_ACTIVE,	/* vdev active on a different host	*/
 } vdev_aux_t;
 
 /*
@@ -764,6 +771,16 @@ typedef enum pool_state {
 	POOL_STATE_POTENTIALLY_ACTIVE	/* Internal libzfs state	*/
 } pool_state_t;
 
+/*
+ * mmp state. The following states provide additional detail describing
+ * why a pool couldn't be safely imported.
+ */
+typedef enum mmp_state {
+	MMP_STATE_ACTIVE = 0,		/* In active use		*/
+	MMP_STATE_INACTIVE,		/* Inactive and safe to import	*/
+	MMP_STATE_NO_HOSTID		/* System hostid is not set	*/
+} mmp_state_t;
+
 /*
  * Scan Functions.
  */
@@ -1126,6 +1143,7 @@ typedef enum {
 #define	ZFS_IMPORT_MISSING_LOG	0x4
 #define	ZFS_IMPORT_ONLY		0x8
 #define	ZFS_IMPORT_TEMP_NAME	0x10
+#define	ZFS_IMPORT_SKIP_MMP	0x20
 
 /*
  * Sysevent payload members.  ZFS will generate the following sysevents with the
diff --git a/include/sys/mmp.h b/include/sys/mmp.h
new file mode 100644
index 000000000000..4da612d6a5a2
--- /dev/null
+++ b/include/sys/mmp.h
@@ -0,0 +1,63 @@
+/*
+ * CDDL HEADER START
+ *
+ * This file and its contents are supplied under the terms of the
+ * Common Development and Distribution License ("CDDL"), version 1.0.
+ * You may only use this file in accordance with the terms of version
+ * 1.0 of the CDDL.
+ *
+ * A full copy of the text of the CDDL should have accompanied this
+ * source.  A copy of the CDDL is also available via the Internet at
+ * http://www.illumos.org/license/CDDL.
+ *
+ * CDDL HEADER END
+ */
+/*
+ * Copyright (C) 2017 by Lawrence Livermore National Security, LLC.
+ */
+
+#ifndef _SYS_MMP_H
+#define	_SYS_MMP_H
+
+#include <sys/spa.h>
+#include <sys/zfs_context.h>
+#include <sys/uberblock_impl.h>
+
+#ifdef	__cplusplus
+extern "C" {
+#endif
+
+#define	MMP_MIN_INTERVAL		100	/* ms */
+#define	MMP_DEFAULT_INTERVAL		1000	/* ms */
+#define	MMP_DEFAULT_IMPORT_INTERVALS	10
+#define	MMP_DEFAULT_FAIL_INTERVALS	5
+
+typedef struct mmp_thread {
+	kmutex_t	mmp_thread_lock; /* protect thread mgmt fields */
+	kcondvar_t	mmp_thread_cv;
+	kthread_t	*mmp_thread;
+	uint8_t		mmp_thread_exiting;
+	kmutex_t	mmp_io_lock;	/* protect below */
+	hrtime_t	mmp_last_write;	/* last successful MMP write */
+	uint64_t	mmp_delay;	/* decaying avg ns between MMP writes */
+	uberblock_t	mmp_ub;		/* last ub written by sync */
+	zio_t		*mmp_zio_root;	/* root of mmp write zios */
+} mmp_thread_t;
+
+
+extern void mmp_init(struct spa *spa);
+extern void mmp_fini(struct spa *spa);
+extern void mmp_thread_start(struct spa *spa);
+extern void mmp_thread_stop(struct spa *spa);
+extern void mmp_update_uberblock(struct spa *spa, struct uberblock *ub);
+
+/* Global tuning */
+extern ulong_t zfs_multihost_interval;
+extern uint_t zfs_multihost_fail_intervals;
+extern uint_t zfs_multihost_import_intervals;
+
+#ifdef	__cplusplus
+}
+#endif
+
+#endif	/* _SYS_MMP_H */
diff --git a/include/sys/spa.h b/include/sys/spa.h
index dd86aad40fe7..de942ad2b5a4 100644
--- a/include/sys/spa.h
+++ b/include/sys/spa.h
@@ -729,6 +729,7 @@ typedef struct spa_stats {
 	spa_stats_history_t	txg_history;
 	spa_stats_history_t	tx_assign_histogram;
 	spa_stats_history_t	io_history;
+	spa_stats_history_t	mmp_history;
 } spa_stats_t;
 
 typedef enum txg_state {
@@ -758,6 +759,8 @@ extern txg_stat_t *spa_txg_history_init_io(spa_t *, uint64_t,
     struct dsl_pool *);
 extern void spa_txg_history_fini_io(spa_t *, txg_stat_t *);
 extern void spa_tx_assign_add_nsecs(spa_t *spa, uint64_t nsecs);
+extern void spa_mmp_history_add(uint64_t txg, uint64_t timestamp,
+    uint64_t mmp_delay, vdev_t *vd, int label);
 
 /* Pool configuration locks */
 extern int spa_config_tryenter(spa_t *spa, int locks, void *tag, krw_t rw);
@@ -860,6 +863,8 @@ extern boolean_t spa_has_pending_synctask(spa_t *spa);
 extern int spa_maxblocksize(spa_t *spa);
 extern int spa_maxdnodesize(spa_t *spa);
 extern void zfs_blkptr_verify(spa_t *spa, const blkptr_t *bp);
+extern boolean_t spa_multihost(spa_t *spa);
+extern unsigned long spa_get_hostid(void);
 
 extern int spa_mode(spa_t *spa);
 extern uint64_t zfs_strtonum(const char *str, char **nptr);
diff --git a/include/sys/spa_impl.h b/include/sys/spa_impl.h
index 9142242cb989..06de244218f3 100644
--- a/include/sys/spa_impl.h
+++ b/include/sys/spa_impl.h
@@ -275,6 +275,8 @@ struct spa {
 	spa_stats_t	spa_stats;		/* assorted spa statistics */
 	hrtime_t	spa_ccw_fail_time;	/* Conf cache write fail time */
 	taskq_t		*spa_zvol_taskq;	/* Taskq for minor management */
+	uint64_t	spa_multihost;		/* multihost aware (mmp) */
+	mmp_thread_t	spa_mmp;		/* multihost mmp thread */
 
 	/*
 	 * spa_refcount & spa_config_lock must be the last elements
diff --git a/include/sys/uberblock.h b/include/sys/uberblock.h
index 21e7ae0de7a7..044e438387c0 100644
--- a/include/sys/uberblock.h
+++ b/include/sys/uberblock.h
@@ -40,7 +40,8 @@ extern "C" {
 typedef struct uberblock uberblock_t;
 
 extern int uberblock_verify(uberblock_t *);
-extern boolean_t uberblock_update(uberblock_t *, vdev_t *, uint64_t);
+extern boolean_t uberblock_update(uberblock_t *ub, vdev_t *rvd, uint64_t txg,
+    uint64_t mmp_delay);
 
 #ifdef	__cplusplus
 }
diff --git a/include/sys/uberblock_impl.h b/include/sys/uberblock_impl.h
index 6ab6aa3135a2..9fdc70b91fc6 100644
--- a/include/sys/uberblock_impl.h
+++ b/include/sys/uberblock_impl.h
@@ -43,6 +43,7 @@ extern "C" {
  */
 #define	UBERBLOCK_MAGIC		0x00bab10c		/* oo-ba-bloc!	*/
 #define	UBERBLOCK_SHIFT		10			/* up to 1K	*/
+#define	MMP_MAGIC		0xa11cea11		/* all-see-all  */
 
 struct uberblock {
 	uint64_t	ub_magic;	/* UBERBLOCK_MAGIC		*/
@@ -54,6 +55,11 @@ struct uberblock {
 
 	/* highest SPA_VERSION supported by software that wrote this txg */
 	uint64_t	ub_software_version;
+
+	/* Maybe missing in uberblocks we read, but always written */
+	uint64_t	ub_mmp_magic;	/* MMP_MAGIC			*/
+	uint64_t	ub_mmp_delay;	/* nanosec since last MMP write	*/
+	uint64_t	ub_mmp_seq;	/* reserved for sequence number	*/
 };
 
 #ifdef	__cplusplus
diff --git a/include/sys/vdev.h b/include/sys/vdev.h
index 63b4904c5e1a..7157ef43f64d 100644
--- a/include/sys/vdev.h
+++ b/include/sys/vdev.h
@@ -155,6 +155,8 @@ extern int vdev_label_number(uint64_t psise, uint64_t offset);
 extern nvlist_t *vdev_label_read_config(vdev_t *vd, uint64_t txg);
 extern void vdev_uberblock_load(vdev_t *, struct uberblock *, nvlist_t **);
 extern void vdev_config_generate_stats(vdev_t *vd, nvlist_t *nv);
+extern void vdev_label_write(zio_t *zio, vdev_t *vd, int l, abd_t *buf, uint64_t
+    offset, uint64_t size, zio_done_func_t *done, void *private, int flags);
 
 typedef enum {
 	VDEV_LABEL_CREATE,	/* create/add a new device */
diff --git a/include/sys/vdev_impl.h b/include/sys/vdev_impl.h
index 835d2dbbf24e..7c5e54b08e19 100644
--- a/include/sys/vdev_impl.h
+++ b/include/sys/vdev_impl.h
@@ -238,6 +238,7 @@ struct vdev {
 	zio_t		*vdev_probe_zio; /* root of current probe	*/
 	vdev_aux_t	vdev_label_aux;	/* on-disk aux state		*/
 	uint64_t	vdev_leaf_zap;
+	hrtime_t	vdev_mmp_pending; /* 0 if write finished	*/
 
 	/*
 	 * For DTrace to work in userland (libzpool) context, these fields must
@@ -268,6 +269,12 @@ struct vdev {
 #define	VDEV_PHYS_SIZE		(112 << 10)
 #define	VDEV_UBERBLOCK_RING	(128 << 10)
 
+/*
+ * MMP blocks occupy the last MMP_BLOCKS_PER_LABEL slots in the uberblock
+ * ring when MMP is enabled.
+ */
+#define	MMP_BLOCKS_PER_LABEL	1
+
 /* The largest uberblock we support is 8k. */
 #define	MAX_UBERBLOCK_SHIFT (13)
 #define	VDEV_UBERBLOCK_SHIFT(vd)	\
diff --git a/lib/libzfs/libzfs_import.c b/lib/libzfs/libzfs_import.c
index 02264433e892..f371d925bc59 100644
--- a/lib/libzfs/libzfs_import.c
+++ b/lib/libzfs/libzfs_import.c
@@ -2166,6 +2166,80 @@ zpool_search_import(libzfs_handle_t *hdl, importargs_t *import)
 	return (zpool_find_import_impl(hdl, import));
 }
 
+static boolean_t
+pool_match(nvlist_t *cfg, char *tgt)
+{
+	uint64_t v, guid = strtoull(tgt, NULL, 0);
+	char *s;
+
+	if (guid != 0) {
+		if (nvlist_lookup_uint64(cfg, ZPOOL_CONFIG_POOL_GUID, &v) == 0)
+			return (v == guid);
+	} else {
+		if (nvlist_lookup_string(cfg, ZPOOL_CONFIG_POOL_NAME, &s) == 0)
+			return (strcmp(s, tgt) == 0);
+	}
+	return (B_FALSE);
+}
+
+int
+zpool_tryimport(libzfs_handle_t *hdl, char *target, nvlist_t **configp,
+    importargs_t *args)
+{
+	nvlist_t *pools;
+	nvlist_t *match = NULL;
+	nvlist_t *config = NULL;
+	char *name = NULL, *sepp = NULL;
+	char sep = '\0';
+	int count = 0;
+	char *targetdup = strdup(target);
+
+	*configp = NULL;
+
+	if ((sepp = strpbrk(targetdup, "/@")) != NULL) {
+		sep = *sepp;
+		*sepp = '\0';
+	}
+
+	pools = zpool_search_import(hdl, args);
+
+	if (pools != NULL) {
+		nvpair_t *elem = NULL;
+		while ((elem = nvlist_next_nvpair(pools, elem)) != NULL) {
+			VERIFY0(nvpair_value_nvlist(elem, &config));
+			if (pool_match(config, targetdup)) {
+				count++;
+				if (match != NULL) {
+					/* multiple matches found */
+					continue;
+				} else {
+					match = config;
+					name = nvpair_name(elem);
+				}
+			}
+		}
+	}
+
+	if (count == 0) {
+		(void) zfs_error_aux(hdl, dgettext(TEXT_DOMAIN,
+		    "no pools found"));
+		free(targetdup);
+		return (ENOENT);
+	}
+
+	if (count > 1) {
+		(void) zfs_error_aux(hdl, dgettext(TEXT_DOMAIN,
+		    "%d pools found, use pool GUID\n"), count);
+		free(targetdup);
+		return (EINVAL);
+	}
+
+	*configp = match;
+	free(targetdup);
+
+	return (0);
+}
+
 boolean_t
 find_guid(nvlist_t *nv, uint64_t guid)
 {
diff --git a/lib/libzfs/libzfs_pool.c b/lib/libzfs/libzfs_pool.c
index 746e6a8cc649..58d91c8f4bb6 100644
--- a/lib/libzfs/libzfs_pool.c
+++ b/lib/libzfs/libzfs_pool.c
@@ -676,7 +676,14 @@ zpool_valid_proplist(libzfs_handle_t *hdl, const char *poolname,
 				goto error;
 			}
 			break;
-
+		case ZPOOL_PROP_MULTIHOST:
+			if (get_system_hostid() == 0) {
+				zfs_error_aux(hdl, dgettext(TEXT_DOMAIN,
+				    "requires a non-zero system hostid"));
+				(void) zfs_error(hdl, EZFS_BADPROP, errbuf);
+				goto error;
+			}
+			break;
 		default:
 			zfs_error_aux(hdl, dgettext(TEXT_DOMAIN,
 			    "property '%s'(%d) not defined"), propname, prop);
@@ -1779,6 +1786,7 @@ zpool_import_props(libzfs_handle_t *hdl, nvlist_t *config, const char *newname,
 
 	if (error) {
 		char desc[1024];
+		char aux[256];
 
 		/*
 		 * Dry-run failed, but we print out what success
@@ -1824,6 +1832,47 @@ zpool_import_props(libzfs_handle_t *hdl, nvlist_t *config, const char *newname,
 			(void) zfs_error(hdl, EZFS_BADVERSION, desc);
 			break;
 
+		case EREMOTEIO:
+			if (nv != NULL && nvlist_lookup_nvlist(nv,
+			    ZPOOL_CONFIG_LOAD_INFO, &nvinfo) == 0) {
+				char *hostname = "<unknown>";
+				uint64_t hostid = 0;
+				mmp_state_t mmp_state;
+
+				mmp_state = fnvlist_lookup_uint64(nvinfo,
+				    ZPOOL_CONFIG_MMP_STATE);
+
+				if (nvlist_exists(nvinfo,
+				    ZPOOL_CONFIG_MMP_HOSTNAME))
+					hostname = fnvlist_lookup_string(nvinfo,
+					    ZPOOL_CONFIG_MMP_HOSTNAME);
+
+				if (nvlist_exists(nvinfo,
+				    ZPOOL_CONFIG_MMP_HOSTID))
+					hostid = fnvlist_lookup_uint64(nvinfo,
+					    ZPOOL_CONFIG_MMP_HOSTID);
+
+				if (mmp_state == MMP_STATE_ACTIVE) {
+					(void) snprintf(aux, sizeof (aux),
+					    dgettext(TEXT_DOMAIN, "pool is imp"
+					    "orted on host '%s' (hostid=%lx).\n"
+					    "Export the pool on the other "
+					    "system, then run 'zpool import'."),
+					    hostname, (unsigned long) hostid);
+				} else if (mmp_state == MMP_STATE_NO_HOSTID) {
+					(void) snprintf(aux, sizeof (aux),
+					    dgettext(TEXT_DOMAIN, "pool has "
+					    "the multihost property on and "
+					    "the\nsystem's hostid is not set. "
+					    "Set a unique system hostid with "
+					    "the genhostid(1) command.\n"));
+				}
+
+				(void) zfs_error_aux(hdl, aux);
+			}
+			(void) zfs_error(hdl, EZFS_ACTIVE_POOL, desc);
+			break;
+
 		case EINVAL:
 			(void) zfs_error(hdl, EZFS_INVALCONFIG, desc);
 			break;
@@ -2206,7 +2255,7 @@ zpool_find_vdev(zpool_handle_t *zhp, const char *path, boolean_t *avail_spare,
 }
 
 static int
-vdev_online(nvlist_t *nv)
+vdev_is_online(nvlist_t *nv)
 {
 	uint64_t ival;
 
@@ -2274,7 +2323,7 @@ vdev_get_physpaths(nvlist_t *nv, char *physpath, size_t phypath_size,
 				return (EZFS_INVALCONFIG);
 		}
 
-		if (vdev_online(nv)) {
+		if (vdev_is_online(nv)) {
 			if ((ret = vdev_get_one_physpath(nv, physpath,
 			    phypath_size, rsz)) != 0)
 				return (ret);
diff --git a/lib/libzfs/libzfs_status.c b/lib/libzfs/libzfs_status.c
index d5470f41238e..05a9afce8a8a 100644
--- a/lib/libzfs/libzfs_status.c
+++ b/lib/libzfs/libzfs_status.c
@@ -64,6 +64,8 @@ static char *zfs_msgid_table[] = {
 	"ZFS-8000-9P",
 	"ZFS-8000-A5",
 	"ZFS-8000-EY",
+	"ZFS-8000-EY",
+	"ZFS-8000-EY",
 	"ZFS-8000-HC",
 	"ZFS-8000-JQ",
 	"ZFS-8000-K4",
@@ -215,6 +217,26 @@ check_status(nvlist_t *config, boolean_t isimport, zpool_errata_t *erratap)
 	    ps->pss_state == DSS_SCANNING)
 		return (ZPOOL_STATUS_RESILVERING);
 
+	/*
+	 * The multihost property is set and the pool may be active.
+	 */
+	if (vs->vs_state == VDEV_STATE_CANT_OPEN &&
+	    vs->vs_aux == VDEV_AUX_ACTIVE) {
+		mmp_state_t mmp_state;
+		nvlist_t *nvinfo;
+
+		nvinfo = fnvlist_lookup_nvlist(config, ZPOOL_CONFIG_LOAD_INFO);
+		mmp_state = fnvlist_lookup_uint64(nvinfo,
+		    ZPOOL_CONFIG_MMP_STATE);
+
+		if (mmp_state == MMP_STATE_ACTIVE)
+			return (ZPOOL_STATUS_HOSTID_ACTIVE);
+		else if (mmp_state == MMP_STATE_NO_HOSTID)
+			return (ZPOOL_STATUS_HOSTID_REQUIRED);
+		else
+			return (ZPOOL_STATUS_HOSTID_MISMATCH);
+	}
+
 	/*
 	 * Pool last accessed by another system.
 	 */
@@ -344,8 +366,9 @@ check_status(nvlist_t *config, boolean_t isimport, zpool_errata_t *erratap)
 		if (isimport) {
 			feat = fnvlist_lookup_nvlist(config,
 			    ZPOOL_CONFIG_LOAD_INFO);
-			feat = fnvlist_lookup_nvlist(feat,
-			    ZPOOL_CONFIG_ENABLED_FEAT);
+			if (nvlist_exists(feat, ZPOOL_CONFIG_ENABLED_FEAT))
+				feat = fnvlist_lookup_nvlist(feat,
+				    ZPOOL_CONFIG_ENABLED_FEAT);
 		} else {
 			feat = fnvlist_lookup_nvlist(config,
 			    ZPOOL_CONFIG_FEATURE_STATS);
diff --git a/lib/libzfs/libzfs_util.c b/lib/libzfs/libzfs_util.c
index 30255d643971..bc51a76a8ecb 100644
--- a/lib/libzfs/libzfs_util.c
+++ b/lib/libzfs/libzfs_util.c
@@ -261,6 +261,9 @@ libzfs_error_description(libzfs_handle_t *hdl)
 		return (dgettext(TEXT_DOMAIN, "invalid diff data"));
 	case EZFS_POOLREADONLY:
 		return (dgettext(TEXT_DOMAIN, "pool is read-only"));
+	case EZFS_ACTIVE_POOL:
+		return (dgettext(TEXT_DOMAIN, "pool is imported on a "
+		    "different host"));
 	case EZFS_UNKNOWN:
 		return (dgettext(TEXT_DOMAIN, "unknown error"));
 	default:
@@ -423,6 +426,9 @@ zfs_standard_error_fmt(libzfs_handle_t *hdl, int error, const char *fmt, ...)
 		    "pool I/O is currently suspended"));
 		zfs_verror(hdl, EZFS_POOLUNAVAIL, fmt, ap);
 		break;
+	case EREMOTEIO:
+		zfs_verror(hdl, EZFS_ACTIVE_POOL, fmt, ap);
+		break;
 	default:
 		zfs_error_aux(hdl, strerror(error));
 		zfs_verror(hdl, EZFS_UNKNOWN, fmt, ap);
@@ -511,6 +517,9 @@ zpool_standard_error_fmt(libzfs_handle_t *hdl, int error, const char *fmt, ...)
 		    "block size out of range or does not match"));
 		zfs_verror(hdl, EZFS_BADPROP, fmt, ap);
 		break;
+	case EREMOTEIO:
+		zfs_verror(hdl, EZFS_ACTIVE_POOL, fmt, ap);
+		break;
 
 	default:
 		zfs_error_aux(hdl, strerror(error));
diff --git a/lib/libzpool/Makefile.am b/lib/libzpool/Makefile.am
index 1e95f8064c8f..a8c72c98de3f 100644
--- a/lib/libzpool/Makefile.am
+++ b/lib/libzpool/Makefile.am
@@ -71,6 +71,7 @@ KERNEL_C = \
 	lzjb.c \
 	lz4.c \
 	metaslab.c \
+	mmp.c \
 	multilist.c \
 	pathname.c \
 	range_tree.c \
diff --git a/man/man1/ztest.1 b/man/man1/ztest.1
index ebfacd46dcb0..8cb07fa99797 100644
--- a/man/man1/ztest.1
+++ b/man/man1/ztest.1
@@ -147,6 +147,12 @@ ztest -f / -V -T 120
 
 .SH "ENVIRONMENT VARIABLES"
 .TP
+.B "ZFS_HOSTID=id"
+Use \fBid\fR instead of the SPL hostid to identify this host.  Intended for use
+with ztest, but this environment variable will affect any utility which uses
+libzpool, including \fBzpool(8)\fR.  Since the kernel is unaware of this setting
+results with utilites other than ztest are undefined.
+.TP
 .B "ZFS_STACK_SIZE=stacksize"
 Limit the default stack size to \fBstacksize\fR bytes for the purpose of
 detecting and debugging kernel stack overflows.  This value defaults to
@@ -160,6 +166,7 @@ required for a NULL procedure in user space.
 
 By default the stack size is limited to 256K.
 .SH "SEE ALSO"
+.BR "spl-module-parameters (5)" ","
 .BR "zpool (1)" ","
 .BR "zfs (1)" ","
 .BR "zdb (1)" ","
diff --git a/man/man5/zfs-module-parameters.5 b/man/man5/zfs-module-parameters.5
index ab1c158413b7..0447debf7322 100644
--- a/man/man5/zfs-module-parameters.5
+++ b/man/man5/zfs-module-parameters.5
@@ -1410,6 +1410,79 @@ otherwise would under the old \fBzfs_mg_alloc_failures\fR facility.
 Default value: \fB0\fR.
 .RE
 
+.sp
+.ne 2
+.na
+\fBzfs_multihost_history\fR (int)
+.ad
+.RS 12n
+Historical statistics for the last N multihost updates will be available in
+\fB/proc/spl/kstat/zfs/<pool>/multihost\fR
+.sp
+Default value: \fB0\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_multihost_interval\fR (ulong)
+.ad
+.RS 12n
+Used to control the frequency of multihost writes which are performed when the
+\fBmultihost\fR pool property is on.  This is one factor used to determine
+the length of the activity check during import.
+.sp
+The multihost write period is \fBzfs_multihost_interval / leaf-vdevs\fR milliseconds.
+This means that on average a multihost write will be issued for each leaf vdev every
+\fBzfs_multihost_interval\fR milliseconds.  In practice, the observed period can
+vary with the I/O load and this observed value is the delay which is stored in
+the uberblock.
+.sp
+On import the activity check waits a minimum amount of time determined by
+\fBzfs_multihost_interval * zfs_multihost_import_intervals\fR.  The activity
+check time may be further extended if the value of mmp delay found in the best
+uberblock indicates actual multihost updates happened at longer intervals than
+\fBzfs_multihost_interval\fR.  A minimum value of \fB100ms\fR is enforced.
+.sp
+Default value: \fB1000\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_multihost_import_intervals\fR (uint)
+.ad
+.RS 12n
+Used to control the duration of the activity test on import.  Smaller values of
+\fBzfs_multihost_import_intervals\fR will reduce the import time but increase
+the risk of failing to detect an active pool.  The total activity check time is
+never allowed to drop below one second.  A value of 0 is ignored and treated as
+if it was set to 1
+.sp
+Default value: \fB10\fR.
+.RE
+
+.sp
+.ne 2
+.na
+\fBzfs_multihost_fail_intervals\fR (uint)
+.ad
+.RS 12n
+Controls the behavior of the pool when multihost write failures are detected.
+.sp
+When \fBzfs_multihost_fail_intervals = 0\fR then multihost write failures are ignored.
+The failures will still be reported to the ZED which depending on its
+configuration may take action such as suspending the pool or offlining a device.
+.sp
+When \fBzfs_multihost_fail_intervals > 0\fR then sequential multihost write failures
+will cause the pool to be suspended.  This occurs when
+\fBzfs_multihost_fail_intervals * zfs_multihost_interval\fR milliseconds have
+passed since the last successful multihost write.  This guarantees the activity test
+will see multihost writes if the pool is imported.
+.sp
+Default value: \fB5\fR.
+.RE
+
 .sp
 .ne 2
 .na
@@ -1529,8 +1602,8 @@ Default value: \fB1,048,576\fR.
 \fBzfs_read_history\fR (int)
 .ad
 .RS 12n
-Historic statistics for the last N reads will be available in
-\fR/proc/spl/kstat/zfs/POOLNAME/reads\fB
+Historical statistics for the last N reads will be available in
+\fB/proc/spl/kstat/zfs/<pool>/reads\fR
 .sp
 Default value: \fB0\fR (no data is kept).
 .RE
@@ -1684,8 +1757,8 @@ Default value: \fB32\fR.
 \fBzfs_txg_history\fR (int)
 .ad
 .RS 12n
-Historic statistics for the last N txgs will be available in
-\fR/proc/spl/kstat/zfs/POOLNAME/txgs\fB
+Historical statistics for the last N txgs will be available in
+\fB/proc/spl/kstat/zfs/<pool>/txgs\fR
 .sp
 Default value: \fB0\fR.
 .RE
diff --git a/man/man8/zpool.8 b/man/man8/zpool.8
index ea25da3000d9..69d77e9610f6 100644
--- a/man/man8/zpool.8
+++ b/man/man8/zpool.8
@@ -717,6 +717,25 @@ The default value is
 .Sy off .
 This property can also be referred to by its shortened name,
 .Sy listsnaps .
+.It Sy multihost Ns = Ns Sy on Ns | Ns Sy off
+Controls whether a pool activity check should be performed during
+.Nm zpool Cm import .
+When a pool is determined to be active it cannot be imported, even with the
+.Fl f
+option.  This property is intended to be used in failover configurations
+where multiple hosts have access to a pool on shared storage.  When this
+property is on, periodic writes to storage occur to show the pool is in use.
+See
+.Sy zfs_multihost_interval
+in the
+.Xr zfs-module-parameters 5
+man page.  In order to enable this property each host must set a unique hostid.
+See
+.Xr genhostid 1
+and
+.Xr spl-module-paramters 5
+for additional details.  The default value is
+.Sy off .
 .It Sy version Ns = Ns Ar version
 The current on-disk version of the pool.
 This can be increased, but never decreased.
@@ -2335,7 +2354,7 @@ is not set, it is assumed that the user is allowed to run
 .Sh INTERFACE STABILITY
 .Sy Evolving
 .Sh SEE ALSO
-.Xr zed 8
+.Xr zed 8 ,
 .Xr zfs 8 ,
 .Xr zfs-events 5 ,
 .Xr zfs-module-parameters 5 ,
diff --git a/module/zcommon/zpool_prop.c b/module/zcommon/zpool_prop.c
index 77b4d62ffde2..fd21f31176a5 100644
--- a/module/zcommon/zpool_prop.c
+++ b/module/zcommon/zpool_prop.c
@@ -120,6 +120,9 @@ zpool_prop_init(void)
 	    PROP_DEFAULT, ZFS_TYPE_POOL, "on | off", "EXPAND", boolean_table);
 	zprop_register_index(ZPOOL_PROP_READONLY, "readonly", 0,
 	    PROP_DEFAULT, ZFS_TYPE_POOL, "on | off", "RDONLY", boolean_table);
+	zprop_register_index(ZPOOL_PROP_MULTIHOST, "multihost", 0,
+	    PROP_DEFAULT, ZFS_TYPE_POOL, "on | off", "MULTIHOST",
+	    boolean_table);
 
 	/* default index properties */
 	zprop_register_index(ZPOOL_PROP_FAILUREMODE, "failmode",
diff --git a/module/zfs/Makefile.in b/module/zfs/Makefile.in
index f8d54f4dde77..d6336f3142ca 100644
--- a/module/zfs/Makefile.in
+++ b/module/zfs/Makefile.in
@@ -43,6 +43,7 @@ $(MODULE)-objs += gzip.o
 $(MODULE)-objs += lzjb.o
 $(MODULE)-objs += lz4.o
 $(MODULE)-objs += metaslab.o
+$(MODULE)-objs += mmp.o
 $(MODULE)-objs += multilist.o
 $(MODULE)-objs += pathname.o
 $(MODULE)-objs += policy.o
diff --git a/module/zfs/dsl_pool.c b/module/zfs/dsl_pool.c
index 97eb0cced707..c16708048cc5 100644
--- a/module/zfs/dsl_pool.c
+++ b/module/zfs/dsl_pool.c
@@ -48,6 +48,7 @@
 #include <sys/zil_impl.h>
 #include <sys/dsl_userhold.h>
 #include <sys/trace_txg.h>
+#include <sys/mmp.h>
 
 /*
  * ZFS Write Throttle
@@ -160,6 +161,7 @@ dsl_pool_open_impl(spa_t *spa, uint64_t txg)
 	dp->dp_meta_rootbp = *bp;
 	rrw_init(&dp->dp_config_rwlock, B_TRUE);
 	txg_init(dp, txg);
+	mmp_init(spa);
 
 	txg_list_create(&dp->dp_dirty_datasets, spa,
 	    offsetof(dsl_dataset_t, ds_dirty_link));
@@ -342,6 +344,7 @@ dsl_pool_close(dsl_pool_t *dp)
 	 */
 	arc_flush(dp->dp_spa, FALSE);
 
+	mmp_fini(dp->dp_spa);
 	txg_fini(dp);
 	dsl_scan_fini(dp);
 	dmu_buf_user_evict_wait();
diff --git a/module/zfs/mmp.c b/module/zfs/mmp.c
new file mode 100644
index 000000000000..35348f8b4dc3
--- /dev/null
+++ b/module/zfs/mmp.c
@@ -0,0 +1,475 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or http://www.opensolaris.org/os/licensing.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+/*
+ * Copyright (c) 2017 by Lawrence Livermore National Security, LLC.
+ */
+
+#include <sys/abd.h>
+#include <sys/mmp.h>
+#include <sys/spa.h>
+#include <sys/spa_impl.h>
+#include <sys/vdev.h>
+#include <sys/vdev_impl.h>
+#include <sys/zfs_context.h>
+#include <sys/callb.h>
+
+/*
+ * Multi-Modifier Protection (MMP) attempts to prevent a user from importing
+ * or opening a pool on more than one host at a time.  In particular, it
+ * prevents "zpool import -f" on a host from succeeding while the pool is
+ * already imported on another host.  There are many other ways in which a
+ * device could be used by two hosts for different purposes at the same time
+ * resulting in pool damage.  This implementation does not attempt to detect
+ * those cases.
+ *
+ * MMP operates by ensuring there are frequent visible changes on disk (a
+ * "heartbeat") at all times.  And by altering the import process to check
+ * for these changes and failing the import when they are detected.  This
+ * functionality is enabled by setting the 'multihost' pool property to on.
+ *
+ * Uberblocks written by the txg_sync thread always go into the first
+ * (N-MMP_BLOCKS_PER_LABEL) slots, the remaining slots are reserved for MMP.
+ * They are used to hold uberblocks which are exactly the same as the last
+ * synced uberblock except that the ub_timestamp is frequently updated.
+ * Like all other uberblocks, the slot is written with an embedded checksum,
+ * and slots with invalid checksums are ignored.  This provides the
+ * "heartbeat", with no risk of overwriting good uberblocks that must be
+ * preserved, e.g. previous txgs and associated block pointers.
+ *
+ * Two optional fields are added to uberblock structure: ub_mmp_magic and
+ * ub_mmp_delay.  The magic field allows zfs to tell whether ub_mmp_delay is
+ * valid.  The delay field is a decaying average of the amount of time between
+ * completion of successive MMP writes, in nanoseconds.  It is used to predict
+ * how long the import must wait to detect activity in the pool, before
+ * concluding it is not in use.
+ *
+ * During import an activity test may now be performed to determine if
+ * the pool is in use.  The activity test is typically required if the
+ * ZPOOL_CONFIG_HOSTID does not match the system hostid, the pool state is
+ * POOL_STATE_ACTIVE, and the pool is not a root pool.
+ *
+ * The activity test finds the "best" uberblock (highest txg & timestamp),
+ * waits some time, and then finds the "best" uberblock again.  If the txg
+ * and timestamp in both "best" uberblocks do not match, the pool is in use
+ * by another host and the import fails.  Since the granularity of the
+ * timestamp is in seconds this activity test must take a bare minimum of one
+ * second.  In order to assure the accuracy of the activity test, the default
+ * values result in an activity test duration of 10x the mmp write interval.
+ *
+ * The "zpool import"  activity test can be expected to take a minimum time of
+ * zfs_multihost_import_intervals * zfs_multihost_interval milliseconds.  If the
+ * "best" uberblock has a valid ub_mmp_delay field, then the duration of the
+ * test may take longer if MMP writes were occurring less frequently than
+ * expected.  Additionally, the duration is then extended by a random 25% to
+ * attempt to to detect simultaneous imports.  For example, if both partner
+ * hosts are rebooted at the same time and automatically attempt to import the
+ * pool.
+ */
+
+/*
+ * Used to control the frequency of mmp writes which are performed when the
+ * 'multihost' pool property is on.  This is one factor used to determine the
+ * length of the activity check during import.
+ *
+ * The mmp write period is zfs_multihost_interval / leaf-vdevs milliseconds.
+ * This means that on average an mmp write will be issued for each leaf vdev
+ * every zfs_multihost_interval milliseconds.  In practice, the observed period
+ * can vary with the I/O load and this observed value is the delay which is
+ * stored in the uberblock.  The minimum allowed value is 100 ms.
+ */
+ulong_t zfs_multihost_interval = MMP_DEFAULT_INTERVAL;
+
+/*
+ * Used to control the duration of the activity test on import.  Smaller values
+ * of zfs_multihost_import_intervals will reduce the import time but increase
+ * the risk of failing to detect an active pool.  The total activity check time
+ * is never allowed to drop below one second.  A value of 0 is ignored and
+ * treated as if it was set to 1.
+ */
+uint_t zfs_multihost_import_intervals = MMP_DEFAULT_IMPORT_INTERVALS;
+
+/*
+ * Controls the behavior of the pool when mmp write failures are detected.
+ *
+ * When zfs_multihost_fail_intervals = 0 then mmp write failures are ignored.
+ * The failures will still be reported to the ZED which depending on its
+ * configuration may take action such as suspending the pool or taking a
+ * device offline.
+ *
+ * When zfs_multihost_fail_intervals > 0 then sequential mmp write failures will
+ * cause the pool to be suspended.  This occurs when
+ * zfs_multihost_fail_intervals * zfs_multihost_interval milliseconds have
+ * passed since the last successful mmp write.  This guarantees the activity
+ * test will see mmp writes if the
+ * pool is imported.
+ */
+uint_t zfs_multihost_fail_intervals = MMP_DEFAULT_FAIL_INTERVALS;
+
+static void mmp_thread(spa_t *spa);
+
+void
+mmp_init(spa_t *spa)
+{
+	mmp_thread_t *mmp = &spa->spa_mmp;
+
+	mutex_init(&mmp->mmp_thread_lock, NULL, MUTEX_DEFAULT, NULL);
+	cv_init(&mmp->mmp_thread_cv, NULL, CV_DEFAULT, NULL);
+	mutex_init(&mmp->mmp_io_lock, NULL, MUTEX_DEFAULT, NULL);
+}
+
+void
+mmp_fini(spa_t *spa)
+{
+	mmp_thread_t *mmp = &spa->spa_mmp;
+
+	mutex_destroy(&mmp->mmp_thread_lock);
+	cv_destroy(&mmp->mmp_thread_cv);
+	mutex_destroy(&mmp->mmp_io_lock);
+}
+
+static void
+mmp_thread_enter(mmp_thread_t *mmp, callb_cpr_t *cpr)
+{
+	CALLB_CPR_INIT(cpr, &mmp->mmp_thread_lock, callb_generic_cpr, FTAG);
+	mutex_enter(&mmp->mmp_thread_lock);
+}
+
+static void
+mmp_thread_exit(mmp_thread_t *mmp, kthread_t **mpp, callb_cpr_t *cpr)
+{
+	ASSERT(*mpp != NULL);
+	*mpp = NULL;
+	cv_broadcast(&mmp->mmp_thread_cv);
+	CALLB_CPR_EXIT(cpr);		/* drops &mmp->mmp_thread_lock */
+	thread_exit();
+}
+
+void
+mmp_thread_start(spa_t *spa)
+{
+	mmp_thread_t *mmp = &spa->spa_mmp;
+
+	if (spa_writeable(spa)) {
+		mutex_enter(&mmp->mmp_thread_lock);
+		if (!mmp->mmp_thread) {
+			dprintf("mmp_thread_start pool %s\n",
+			    spa->spa_name);
+			mmp->mmp_thread = thread_create(NULL, 0, mmp_thread,
+			    spa, 0, &p0, TS_RUN, defclsyspri);
+		}
+		mutex_exit(&mmp->mmp_thread_lock);
+	}
+}
+
+void
+mmp_thread_stop(spa_t *spa)
+{
+	mmp_thread_t *mmp = &spa->spa_mmp;
+
+	mutex_enter(&mmp->mmp_thread_lock);
+	mmp->mmp_thread_exiting = 1;
+	cv_broadcast(&mmp->mmp_thread_cv);
+
+	while (mmp->mmp_thread) {
+		cv_wait(&mmp->mmp_thread_cv, &mmp->mmp_thread_lock);
+	}
+	mutex_exit(&mmp->mmp_thread_lock);
+
+	ASSERT(mmp->mmp_thread == NULL);
+	mmp->mmp_thread_exiting = 0;
+}
+
+/*
+ * Randomly choose a leaf vdev, to write an MMP block to.  It must be
+ * writable.  It must not have an outstanding mmp write (if so then
+ * there is a problem, and a new write will also block).
+ *
+ * We try 10 times to pick a random leaf without an outstanding write.
+ * If 90% of the leaves have pending writes, this gives us a >65%
+ * chance of finding one we can write to.  There will be at least
+ * (zfs_multihost_fail_intervals) tries before the inability to write an MMP
+ * block causes serious problems.
+ */
+static vdev_t *
+vdev_random_leaf(spa_t *spa)
+{
+	vdev_t *vd, *child;
+	int pending_writes = 10;
+
+	ASSERT(spa);
+	ASSERT(spa_config_held(spa, SCL_STATE, RW_READER) == SCL_STATE);
+
+	/*
+	 * Since we hold SCL_STATE, neither pool nor vdev state can
+	 * change.  Therefore, if the root is not dead, there is a
+	 * child that is not dead, and so on down to a leaf.
+	 */
+	if (!vdev_writeable(spa->spa_root_vdev))
+		return (NULL);
+
+	vd = spa->spa_root_vdev;
+	while (!vd->vdev_ops->vdev_op_leaf) {
+		child = vd->vdev_child[spa_get_random(vd->vdev_children)];
+
+		if (!vdev_writeable(child))
+			continue;
+
+		if (child->vdev_ops->vdev_op_leaf && child->vdev_mmp_pending) {
+			if (pending_writes-- > 0)
+				continue;
+			else
+				return (NULL);
+		}
+
+		vd = child;
+	}
+	return (vd);
+}
+
+static void
+mmp_write_done(zio_t *zio)
+{
+	spa_t *spa = zio->io_spa;
+	vdev_t *vd = zio->io_vd;
+	mmp_thread_t *mts = zio->io_private;
+
+	mutex_enter(&mts->mmp_io_lock);
+	vd->vdev_mmp_pending = 0;
+
+	if (zio->io_error)
+		goto unlock;
+
+	/*
+	 * Mmp writes are queued on a fixed schedule, but under many
+	 * circumstances, such as a busy device or faulty hardware,
+	 * the writes will complete at variable, much longer,
+	 * intervals.  In these cases, another node checking for
+	 * activity must wait longer to account for these delays.
+	 *
+	 * The mmp_delay is calculated as a decaying average of the interval
+	 * between completed mmp writes.  This is used to predict how long
+	 * the import must wait to detect activity in the pool, before
+	 * concluding it is not in use.
+	 *
+	 * Do not set mmp_delay if the multihost property is not on,
+	 * so as not to trigger an activity check on import.
+	 */
+	if (spa_multihost(spa)) {
+		hrtime_t delay = gethrtime() - mts->mmp_last_write;
+
+		if (delay > mts->mmp_delay)
+			mts->mmp_delay = delay;
+		else
+			mts->mmp_delay = (delay + mts->mmp_delay * 127) /
+			    128;
+	} else {
+		mts->mmp_delay = 0;
+	}
+	mts->mmp_last_write = gethrtime();
+
+unlock:
+	mutex_exit(&mts->mmp_io_lock);
+
+	abd_free(zio->io_abd);
+}
+
+/*
+ * When the uberblock on-disk is updated by a spa_sync,
+ * creating a new "best" uberblock, update the one stored
+ * in the mmp thread state, used for mmp writes.
+ */
+void
+mmp_update_uberblock(spa_t *spa, uberblock_t *ub)
+{
+	mmp_thread_t *mmp = &spa->spa_mmp;
+
+	mutex_enter(&mmp->mmp_io_lock);
+	mmp->mmp_ub = *ub;
+	mmp->mmp_ub.ub_timestamp = gethrestime_sec();
+	mutex_exit(&mmp->mmp_io_lock);
+}
+
+/*
+ * Choose a random vdev, label, and MMP block, and write over it
+ * with a copy of the last-synced uberblock, whose timestamp
+ * has been updated to reflect that the pool is in use.
+ */
+static void
+mmp_write_uberblock(spa_t *spa)
+{
+	int flags = ZIO_FLAG_CONFIG_WRITER | ZIO_FLAG_CANFAIL;
+	mmp_thread_t *mmp = &spa->spa_mmp;
+	uberblock_t *ub;
+	vdev_t *vd;
+	int label;
+	uint64_t offset;
+
+	vd = vdev_random_leaf(spa);
+	if (vd == NULL || !vdev_writeable(vd))
+		return;
+
+	mutex_enter(&mmp->mmp_io_lock);
+
+	if (mmp->mmp_zio_root == NULL)
+		mmp->mmp_zio_root = zio_root(spa, NULL, NULL,
+		    flags | ZIO_FLAG_GODFATHER);
+
+	ub = &mmp->mmp_ub;
+	ub->ub_timestamp = gethrestime_sec();
+	ub->ub_mmp_magic = MMP_MAGIC;
+	ub->ub_mmp_delay = mmp->mmp_delay;
+	vd->vdev_mmp_pending = gethrtime();
+
+	zio_t *zio  = zio_null(mmp->mmp_zio_root, spa, NULL, NULL, NULL, flags);
+	abd_t *ub_abd = abd_alloc_for_io(VDEV_UBERBLOCK_SIZE(vd), B_TRUE);
+	abd_zero(ub_abd, VDEV_UBERBLOCK_SIZE(vd));
+	abd_copy_from_buf(ub_abd, ub, sizeof (uberblock_t));
+
+	mutex_exit(&mmp->mmp_io_lock);
+
+	offset = VDEV_UBERBLOCK_OFFSET(vd, VDEV_UBERBLOCK_COUNT(vd) -
+	    MMP_BLOCKS_PER_LABEL + spa_get_random(MMP_BLOCKS_PER_LABEL));
+
+	label = spa_get_random(VDEV_LABELS);
+	vdev_label_write(zio, vd, label, ub_abd, offset,
+	    VDEV_UBERBLOCK_SIZE(vd), mmp_write_done, mmp,
+	    flags | ZIO_FLAG_DONT_PROPAGATE);
+
+	spa_mmp_history_add(ub->ub_txg, ub->ub_timestamp, ub->ub_mmp_delay, vd,
+	    label);
+
+	zio_nowait(zio);
+}
+
+static void
+mmp_thread(spa_t *spa)
+{
+	mmp_thread_t *mmp = &spa->spa_mmp;
+	boolean_t last_spa_suspended = spa_suspended(spa);
+	boolean_t last_spa_multihost = spa_multihost(spa);
+	callb_cpr_t cpr;
+	hrtime_t max_fail_ns = zfs_multihost_fail_intervals *
+	    MSEC2NSEC(MAX(zfs_multihost_interval, MMP_MIN_INTERVAL));
+
+	mmp_thread_enter(mmp, &cpr);
+
+	/*
+	 * The mmp_write_done() function calculates mmp_delay based on the
+	 * prior value of mmp_delay and the elapsed time since the last write.
+	 * For the first mmp write, there is no "last write", so we start
+	 * with fake, but reasonable, default non-zero values.
+	 */
+	mmp->mmp_delay = MSEC2NSEC(MAX(zfs_multihost_interval,
+	    MMP_MIN_INTERVAL)) / vdev_count_leaves(spa);
+	mmp->mmp_last_write = gethrtime() - mmp->mmp_delay;
+
+	while (!mmp->mmp_thread_exiting) {
+		uint64_t mmp_fail_intervals = zfs_multihost_fail_intervals;
+		uint64_t mmp_interval = MSEC2NSEC(
+		    MAX(zfs_multihost_interval, MMP_MIN_INTERVAL));
+		boolean_t suspended = spa_suspended(spa);
+		boolean_t multihost = spa_multihost(spa);
+		hrtime_t start, next_time;
+
+		start = gethrtime();
+		if (multihost) {
+			next_time = start + mmp_interval /
+			    vdev_count_leaves(spa);
+		} else {
+			next_time = start + MSEC2NSEC(MMP_DEFAULT_INTERVAL);
+		}
+
+		/*
+		 * When MMP goes off => on, or spa goes suspended =>
+		 * !suspended, we know no writes occurred recently.  We
+		 * update mmp_last_write to give us some time to try.
+		 */
+		if ((!last_spa_multihost && multihost) ||
+		    (last_spa_suspended && !suspended)) {
+			mutex_enter(&mmp->mmp_io_lock);
+			mmp->mmp_last_write = gethrtime();
+			mutex_exit(&mmp->mmp_io_lock);
+		} else if (last_spa_multihost && !multihost) {
+			mutex_enter(&mmp->mmp_io_lock);
+			mmp->mmp_delay = 0;
+			mutex_exit(&mmp->mmp_io_lock);
+		}
+		last_spa_multihost = multihost;
+		last_spa_suspended = suspended;
+
+		/*
+		 * Smooth max_fail_ns when its factors are decreased, because
+		 * making (max_fail_ns < mmp_interval) results in the pool being
+		 * immediately suspended before writes can occur at the new
+		 * higher frequency.
+		 */
+		if ((mmp_interval * mmp_fail_intervals) < max_fail_ns) {
+			max_fail_ns = ((31 * max_fail_ns) + (mmp_interval *
+			    mmp_fail_intervals)) / 32;
+		} else {
+			max_fail_ns = mmp_interval * mmp_fail_intervals;
+		}
+
+		/*
+		 * Suspend the pool if no MMP write has succeeded in over
+		 * mmp_interval * mmp_fail_intervals nanoseconds.
+		 */
+		if (!suspended && mmp_fail_intervals && multihost &&
+		    (start - mmp->mmp_last_write) > max_fail_ns) {
+			zio_suspend(spa, NULL);
+		}
+
+		if (multihost) {
+			spa_config_enter(spa, SCL_STATE, FTAG, RW_READER);
+			mmp_write_uberblock(spa);
+			spa_config_exit(spa, SCL_STATE, FTAG);
+		}
+
+		CALLB_CPR_SAFE_BEGIN(&cpr);
+		(void) cv_timedwait_sig(&mmp->mmp_thread_cv,
+		    &mmp->mmp_thread_lock, ddi_get_lbolt() +
+		    ((next_time - gethrtime()) / (NANOSEC / HZ)));
+		CALLB_CPR_SAFE_END(&cpr, &mmp->mmp_thread_lock);
+	}
+
+	/* Outstanding writes are allowed to complete. */
+	if (mmp->mmp_zio_root)
+		zio_wait(mmp->mmp_zio_root);
+
+	mmp->mmp_zio_root = NULL;
+	mmp_thread_exit(mmp, &mmp->mmp_thread, &cpr);
+}
+
+#if defined(_KERNEL) && defined(HAVE_SPL)
+/* BEGIN CSTYLED */
+module_param(zfs_multihost_fail_intervals, uint, 0644);
+MODULE_PARM_DESC(zfs_multihost_fail_intervals,
+	"Max allowed period without a successful mmp write");
+
+module_param(zfs_multihost_interval, ulong, 0644);
+MODULE_PARM_DESC(zfs_multihost_interval,
+	"Milliseconds between mmp writes to each leaf");
+
+module_param(zfs_multihost_import_intervals, uint, 0644);
+MODULE_PARM_DESC(zfs_multihost_import_intervals,
+	"Number of zfs_multihost_interval periods to wait for activity");
+/* END CSTYLED */
+#endif
diff --git a/module/zfs/spa.c b/module/zfs/spa.c
index 52420194c536..7edf0459ce47 100644
--- a/module/zfs/spa.c
+++ b/module/zfs/spa.c
@@ -55,6 +55,7 @@
 #include <sys/vdev_disk.h>
 #include <sys/metaslab.h>
 #include <sys/metaslab_impl.h>
+#include <sys/mmp.h>
 #include <sys/uberblock_impl.h>
 #include <sys/txg.h>
 #include <sys/avl.h>
@@ -491,6 +492,16 @@ spa_prop_validate(spa_t *spa, nvlist_t *props)
 				error = SET_ERROR(EINVAL);
 			break;
 
+		case ZPOOL_PROP_MULTIHOST:
+			error = nvpair_value_uint64(elem, &intval);
+			if (!error && intval > 1)
+				error = SET_ERROR(EINVAL);
+
+			if (!error && !spa_get_hostid())
+				error = SET_ERROR(ENOTSUP);
+
+			break;
+
 		case ZPOOL_PROP_BOOTFS:
 			/*
 			 * If the pool version is less than SPA_VERSION_BOOTFS,
@@ -1346,6 +1357,9 @@ spa_unload(spa_t *spa)
 		spa_config_exit(spa, SCL_ALL, FTAG);
 	}
 
+	if (spa->spa_mmp.mmp_thread)
+		mmp_thread_stop(spa);
+
 	/*
 	 * Wait for any outstanding async I/O to complete.
 	 */
@@ -2323,6 +2337,197 @@ vdev_count_verify_zaps(vdev_t *vd)
 }
 #endif
 
+/*
+ * Determine whether the activity check is required.
+ */
+static boolean_t
+spa_activity_check_required(spa_t *spa, uberblock_t *ub, nvlist_t *config)
+{
+	uint64_t state = 0;
+	uint64_t hostid = 0;
+	uint64_t tryconfig_txg = 0;
+	uint64_t tryconfig_timestamp = 0;
+	nvlist_t *nvinfo;
+
+	if (nvlist_exists(config, ZPOOL_CONFIG_LOAD_INFO)) {
+		nvinfo = fnvlist_lookup_nvlist(config, ZPOOL_CONFIG_LOAD_INFO);
+		(void) nvlist_lookup_uint64(nvinfo, ZPOOL_CONFIG_MMP_TXG,
+		    &tryconfig_txg);
+		(void) nvlist_lookup_uint64(config, ZPOOL_CONFIG_TIMESTAMP,
+		    &tryconfig_timestamp);
+	}
+
+	(void) nvlist_lookup_uint64(config, ZPOOL_CONFIG_POOL_STATE, &state);
+	(void) nvlist_lookup_uint64(config, ZPOOL_CONFIG_HOSTID, &hostid);
+
+	/*
+	 * Disable the MMP activity check - This is used by zdb which
+	 * is intended to be used on potentially active pools.
+	 */
+	if (spa->spa_import_flags & ZFS_IMPORT_SKIP_MMP)
+		return (B_FALSE);
+
+	/*
+	 * Skip the activity check when the MMP feature is disabled.
+	 */
+	if (ub->ub_mmp_magic == MMP_MAGIC && ub->ub_mmp_delay == 0)
+		return (B_FALSE);
+	/*
+	 * If the tryconfig_* values are nonzero, they are the results of an
+	 * earlier tryimport.  If they match the uberblock we just found, then
+	 * the pool has not changed and we return false so we do not test a
+	 * second time.
+	 */
+	if (tryconfig_txg && tryconfig_txg == ub->ub_txg &&
+	    tryconfig_timestamp && tryconfig_timestamp == ub->ub_timestamp)
+		return (B_FALSE);
+
+	/*
+	 * Allow the activity check to be skipped when importing the pool
+	 * on the same host which last imported it.
+	 */
+	if (hostid == spa_get_hostid())
+		return (B_FALSE);
+
+	/*
+	 * Skip the activity test when the pool was cleanly exported.
+	 */
+	if (state != POOL_STATE_ACTIVE)
+		return (B_FALSE);
+
+	return (B_TRUE);
+}
+
+/*
+ * Perform the import activity check.  If the user canceled the import or
+ * we detected activity then fail.
+ */
+static int
+spa_activity_check(spa_t *spa, uberblock_t *ub, nvlist_t *config)
+{
+	uint64_t import_intervals = MAX(zfs_multihost_import_intervals, 1);
+	uint64_t txg = ub->ub_txg;
+	uint64_t timestamp = ub->ub_timestamp;
+	uint64_t import_delay = NANOSEC;
+	hrtime_t import_expire;
+	nvlist_t *mmp_label = NULL;
+	vdev_t *rvd = spa->spa_root_vdev;
+	kcondvar_t cv;
+	kmutex_t mtx;
+	int error = 0;
+
+	cv_init(&cv, NULL, CV_DEFAULT, NULL);
+	mutex_init(&mtx, NULL, MUTEX_DEFAULT, NULL);
+	mutex_enter(&mtx);
+
+	/*
+	 * If ZPOOL_CONFIG_MMP_TXG is present an activity check was performed
+	 * during the earlier tryimport.  If the txg recorded there is 0 then
+	 * the pool is known to be active on another host.
+	 *
+	 * Otherwise, the pool might be in use on another node.  Check for
+	 * changes in the uberblocks on disk if necessary.
+	 */
+	if (nvlist_exists(config, ZPOOL_CONFIG_LOAD_INFO)) {
+		nvlist_t *nvinfo = fnvlist_lookup_nvlist(config,
+		    ZPOOL_CONFIG_LOAD_INFO);
+
+		if (nvlist_exists(nvinfo, ZPOOL_CONFIG_MMP_TXG) &&
+		    fnvlist_lookup_uint64(nvinfo, ZPOOL_CONFIG_MMP_TXG) == 0) {
+			vdev_uberblock_load(rvd, ub, &mmp_label);
+			error = SET_ERROR(EREMOTEIO);
+			goto out;
+		}
+	}
+
+	/*
+	 * Preferentially use the zfs_multihost_interval from the node which
+	 * last imported the pool.  This value is stored in an MMP uberblock as.
+	 *
+	 * ub_mmp_delay * vdev_count_leaves() == zfs_multihost_interval
+	 */
+	if (ub->ub_mmp_magic == MMP_MAGIC && ub->ub_mmp_delay)
+		import_delay = MAX(import_delay, import_intervals *
+		    ub->ub_mmp_delay * vdev_count_leaves(spa));
+
+	/* Apply a floor using the local default values. */
+	import_delay = MAX(import_delay, import_intervals *
+	    MSEC2NSEC(MAX(zfs_multihost_interval, MMP_MIN_INTERVAL)));
+
+	/* Add a small random factor in case of simultaneous imports (0-25%) */
+	import_expire = gethrtime() + import_delay +
+	    (import_delay * spa_get_random(250) / 1000);
+
+	while (gethrtime() < import_expire) {
+		vdev_uberblock_load(rvd, ub, &mmp_label);
+
+		if (txg != ub->ub_txg || timestamp != ub->ub_timestamp) {
+			error = SET_ERROR(EREMOTEIO);
+			break;
+		}
+
+		if (mmp_label) {
+			nvlist_free(mmp_label);
+			mmp_label = NULL;
+		}
+
+		error = cv_timedwait_sig(&cv, &mtx, ddi_get_lbolt() + hz);
+		if (error != -1) {
+			error = SET_ERROR(EINTR);
+			break;
+		}
+		error = 0;
+	}
+
+out:
+	mutex_exit(&mtx);
+	mutex_destroy(&mtx);
+	cv_destroy(&cv);
+
+	/*
+	 * If the pool is determined to be active store the status in the
+	 * spa->spa_load_info nvlist.  If the remote hostname or hostid are
+	 * available from configuration read from disk store them as well.
+	 * This allows 'zpool import' to generate a more useful message.
+	 *
+	 * ZPOOL_CONFIG_MMP_STATE    - observed pool status (mandatory)
+	 * ZPOOL_CONFIG_MMP_HOSTNAME - hostname from the active pool
+	 * ZPOOL_CONFIG_MMP_HOSTID   - hostid from the active pool
+	 */
+	if (error == EREMOTEIO) {
+		char *hostname = "<unknown>";
+		uint64_t hostid = 0;
+
+		if (mmp_label) {
+			if (nvlist_exists(mmp_label, ZPOOL_CONFIG_HOSTNAME)) {
+				hostname = fnvlist_lookup_string(mmp_label,
+				    ZPOOL_CONFIG_HOSTNAME);
+				fnvlist_add_string(spa->spa_load_info,
+				    ZPOOL_CONFIG_MMP_HOSTNAME, hostname);
+			}
+
+			if (nvlist_exists(mmp_label, ZPOOL_CONFIG_HOSTID)) {
+				hostid = fnvlist_lookup_uint64(mmp_label,
+				    ZPOOL_CONFIG_HOSTID);
+				fnvlist_add_uint64(spa->spa_load_info,
+				    ZPOOL_CONFIG_MMP_HOSTID, hostid);
+			}
+		}
+
+		fnvlist_add_uint64(spa->spa_load_info,
+		    ZPOOL_CONFIG_MMP_STATE, MMP_STATE_ACTIVE);
+		fnvlist_add_uint64(spa->spa_load_info,
+		    ZPOOL_CONFIG_MMP_TXG, 0);
+
+		error = spa_vdev_err(rvd, VDEV_AUX_ACTIVE, EREMOTEIO);
+	}
+
+	if (mmp_label)
+		nvlist_free(mmp_label);
+
+	return (error);
+}
+
 /*
  * Load an existing storage pool, using the pool's builtin spa_config as a
  * source of configuration information.
@@ -2343,6 +2548,7 @@ spa_load_impl(spa_t *spa, uint64_t pool_guid, nvlist_t *config,
 	int parse, i;
 	uint64_t obj;
 	boolean_t missing_feat_write = B_FALSE;
+	boolean_t activity_check = B_FALSE;
 	nvlist_t *mos_config;
 
 	/*
@@ -2440,6 +2646,33 @@ spa_load_impl(spa_t *spa, uint64_t pool_guid, nvlist_t *config,
 		return (spa_vdev_err(rvd, VDEV_AUX_CORRUPT_DATA, ENXIO));
 	}
 
+	/*
+	 * For pools which have the multihost property on determine if the
+	 * pool is truly inactive and can be safely imported.  Prevent
+	 * hosts which don't have a hostid set from importing the pool.
+	 */
+	activity_check = spa_activity_check_required(spa, ub, config);
+	if (activity_check) {
+		error = spa_activity_check(spa, ub, config);
+		if (error) {
+			nvlist_free(label);
+			return (error);
+		}
+
+		if (ub->ub_mmp_magic == MMP_MAGIC && ub->ub_mmp_delay &&
+		    spa_get_hostid() == 0) {
+			nvlist_free(label);
+			fnvlist_add_uint64(spa->spa_load_info,
+			    ZPOOL_CONFIG_MMP_STATE, MMP_STATE_NO_HOSTID);
+			return (spa_vdev_err(rvd, VDEV_AUX_ACTIVE, EREMOTEIO));
+		}
+
+		fnvlist_add_uint64(spa->spa_load_info,
+		    ZPOOL_CONFIG_MMP_STATE, MMP_STATE_INACTIVE);
+		fnvlist_add_uint64(spa->spa_load_info,
+		    ZPOOL_CONFIG_MMP_TXG, ub->ub_txg);
+	}
+
 	/*
 	 * If the pool has an unsupported version we can't open it.
 	 */
@@ -2667,24 +2900,9 @@ spa_load_impl(spa_t *spa, uint64_t pool_guid, nvlist_t *config,
 			VERIFY(nvlist_lookup_string(nvconfig,
 			    ZPOOL_CONFIG_HOSTNAME, &hostname) == 0);
 
-#ifdef	_KERNEL
-			myhostid = zone_get_hostid(NULL);
-#else	/* _KERNEL */
-			/*
-			 * We're emulating the system's hostid in userland, so
-			 * we can't use zone_get_hostid().
-			 */
-			(void) ddi_strtoul(hw_serial, NULL, 10, &myhostid);
-#endif	/* _KERNEL */
-			if (hostid != 0 && myhostid != 0 &&
-			    hostid != myhostid) {
+			myhostid = spa_get_hostid();
+			if (hostid && myhostid && hostid != myhostid) {
 				nvlist_free(nvconfig);
-				cmn_err(CE_WARN, "pool '%s' could not be "
-				    "loaded as it was last accessed by another "
-				    "system (host: %s hostid: 0x%lx). See: "
-				    "http://zfsonlinux.org/msg/ZFS-8000-EY",
-				    spa_name(spa), hostname,
-				    (unsigned long)hostid);
 				return (SET_ERROR(EBADF));
 			}
 		}
@@ -2850,12 +3068,25 @@ spa_load_impl(spa_t *spa, uint64_t pool_guid, nvlist_t *config,
 		spa_prop_find(spa, ZPOOL_PROP_DELEGATION, &spa->spa_delegation);
 		spa_prop_find(spa, ZPOOL_PROP_FAILUREMODE, &spa->spa_failmode);
 		spa_prop_find(spa, ZPOOL_PROP_AUTOEXPAND, &spa->spa_autoexpand);
+		spa_prop_find(spa, ZPOOL_PROP_MULTIHOST, &spa->spa_multihost);
 		spa_prop_find(spa, ZPOOL_PROP_DEDUPDITTO,
 		    &spa->spa_dedup_ditto);
 
 		spa->spa_autoreplace = (autoreplace != 0);
 	}
 
+	/*
+	 * If the 'multihost' property is set, then never allow a pool to
+	 * be imported when the system hostid is zero.  The exception to
+	 * this rule is zdb which is always allowed to access pools.
+	 */
+	if (spa_multihost(spa) && spa_get_hostid() == 0 &&
+	    (spa->spa_import_flags & ZFS_IMPORT_SKIP_MMP) == 0) {
+		fnvlist_add_uint64(spa->spa_load_info,
+		    ZPOOL_CONFIG_MMP_STATE, MMP_STATE_NO_HOSTID);
+		return (spa_vdev_err(rvd, VDEV_AUX_ACTIVE, EREMOTEIO));
+	}
+
 	/*
 	 * If the 'autoreplace' property is set, then post a resource notifying
 	 * the ZFS DE that it should not issue any faults for unopenable
@@ -2980,6 +3211,7 @@ spa_load_impl(spa_t *spa, uint64_t pool_guid, nvlist_t *config,
 		spa_set_log_state(spa, SPA_LOG_GOOD);
 		spa->spa_sync_on = B_TRUE;
 		txg_sync_start(spa->spa_dsl_pool);
+		mmp_thread_start(spa);
 
 		/*
 		 * Wait for all claims to sync.  We sync up to the highest
@@ -3632,18 +3864,6 @@ spa_validate_aux_devs(spa_t *spa, nvlist_t *nvroot, uint64_t crtxg, int mode,
 			goto out;
 		}
 
-		/*
-		 * The L2ARC currently only supports disk devices in
-		 * kernel context.  For user-level testing, we allow it.
-		 */
-#ifdef _KERNEL
-		if ((strcmp(config, ZPOOL_CONFIG_L2CACHE) == 0) &&
-		    strcmp(vd->vdev_ops->vdev_op_type, VDEV_TYPE_DISK) != 0) {
-			error = SET_ERROR(ENOTBLK);
-			vdev_free(vd);
-			goto out;
-		}
-#endif
 		vd->vdev_top = vd;
 
 		if ((error = vdev_open(vd)) == 0 &&
@@ -3986,6 +4206,7 @@ spa_create(const char *pool, nvlist_t *nvroot, nvlist_t *props,
 	spa->spa_delegation = zpool_prop_default_numeric(ZPOOL_PROP_DELEGATION);
 	spa->spa_failmode = zpool_prop_default_numeric(ZPOOL_PROP_FAILUREMODE);
 	spa->spa_autoexpand = zpool_prop_default_numeric(ZPOOL_PROP_AUTOEXPAND);
+	spa->spa_multihost = zpool_prop_default_numeric(ZPOOL_PROP_MULTIHOST);
 
 	if (props != NULL) {
 		spa_configfile_set(spa, props, B_FALSE);
@@ -3996,6 +4217,7 @@ spa_create(const char *pool, nvlist_t *nvroot, nvlist_t *props,
 
 	spa->spa_sync_on = B_TRUE;
 	txg_sync_start(spa->spa_dsl_pool);
+	mmp_thread_start(spa);
 
 	/*
 	 * We explicitly wait for the first transaction to complete so that our
@@ -6405,6 +6627,9 @@ spa_sync_props(void *arg, dmu_tx_t *tx)
 					spa_async_request(spa,
 					    SPA_ASYNC_AUTOEXPAND);
 				break;
+			case ZPOOL_PROP_MULTIHOST:
+				spa->spa_multihost = intval;
+				break;
 			case ZPOOL_PROP_DEDUPDITTO:
 				spa->spa_dedup_ditto = intval;
 				break;
diff --git a/module/zfs/spa_config.c b/module/zfs/spa_config.c
index 2715898cc09e..5b792b868455 100644
--- a/module/zfs/spa_config.c
+++ b/module/zfs/spa_config.c
@@ -436,15 +436,7 @@ spa_config_generate(spa_t *spa, vdev_t *vd, uint64_t txg, int getstats)
 		fnvlist_add_string(config, ZPOOL_CONFIG_COMMENT,
 		    spa->spa_comment);
 
-#ifdef	_KERNEL
-	hostid = zone_get_hostid(NULL);
-#else	/* _KERNEL */
-	/*
-	 * We're emulating the system's hostid in userland, so we can't use
-	 * zone_get_hostid().
-	 */
-	(void) ddi_strtoul(hw_serial, NULL, 10, &hostid);
-#endif	/* _KERNEL */
+	hostid = spa_get_hostid();
 	if (hostid != 0)
 		fnvlist_add_uint64(config, ZPOOL_CONFIG_HOSTID, hostid);
 	fnvlist_add_string(config, ZPOOL_CONFIG_HOSTNAME, utsname()->nodename);
diff --git a/module/zfs/spa_misc.c b/module/zfs/spa_misc.c
index 09e5067a54e4..3787e010f60a 100644
--- a/module/zfs/spa_misc.c
+++ b/module/zfs/spa_misc.c
@@ -1384,6 +1384,9 @@ spa_get_random(uint64_t range)
 
 	ASSERT(range != 0);
 
+	if (range == 1)
+		return (0);
+
 	(void) random_get_pseudo_bytes((void *)&r, sizeof (uint64_t));
 
 	return (r % range);
@@ -2073,6 +2076,30 @@ spa_maxdnodesize(spa_t *spa)
 		return (DNODE_MIN_SIZE);
 }
 
+boolean_t
+spa_multihost(spa_t *spa)
+{
+	return (spa->spa_multihost ? B_TRUE : B_FALSE);
+}
+
+unsigned long
+spa_get_hostid(void)
+{
+	unsigned long myhostid;
+
+#ifdef	_KERNEL
+	myhostid = zone_get_hostid(NULL);
+#else	/* _KERNEL */
+	/*
+	 * We're emulating the system's hostid in userland, so
+	 * we can't use zone_get_hostid().
+	 */
+	(void) ddi_strtoul(hw_serial, NULL, 10, &myhostid);
+#endif	/* _KERNEL */
+
+	return (myhostid);
+}
+
 #if defined(_KERNEL) && defined(HAVE_SPL)
 /* Namespace manipulation */
 EXPORT_SYMBOL(spa_lookup);
diff --git a/module/zfs/spa_stats.c b/module/zfs/spa_stats.c
index ac1fb8c6f555..7ca359806174 100644
--- a/module/zfs/spa_stats.c
+++ b/module/zfs/spa_stats.c
@@ -21,6 +21,7 @@
 
 #include <sys/zfs_context.h>
 #include <sys/spa_impl.h>
+#include <sys/vdev_impl.h>
 
 /*
  * Keeps stats on last N reads per spa_t, disabled by default.
@@ -37,6 +38,11 @@ int zfs_read_history_hits = 0;
  */
 int zfs_txg_history = 0;
 
+/*
+ * Keeps stats on the last N MMP updates, disabled by default.
+ */
+int zfs_multihost_history = 0;
+
 /*
  * ==========================================================================
  * SPA Read History Routines
@@ -701,6 +707,198 @@ spa_io_history_destroy(spa_t *spa)
 	mutex_destroy(&ssh->lock);
 }
 
+/*
+ * ==========================================================================
+ * SPA MMP History Routines
+ * ==========================================================================
+ */
+
+/*
+ * MMP statistics - Information exported regarding each MMP update
+ */
+
+typedef struct spa_mmp_history {
+	uint64_t	txg;		/* txg of last sync */
+	uint64_t	timestamp;	/* UTC time of of last sync */
+	uint64_t	mmp_delay;	/* nanosec since last MMP write */
+	uint64_t	vdev_guid;	/* unique ID of leaf vdev */
+	char		*vdev_path;
+	uint64_t	vdev_label;	/* vdev label */
+	list_node_t	smh_link;
+} spa_mmp_history_t;
+
+static int
+spa_mmp_history_headers(char *buf, size_t size)
+{
+	(void) snprintf(buf, size, "%-10s %-10s %-12s %-24s %-10s %s\n",
+	    "txg", "timestamp", "mmp_delay", "vdev_guid", "vdev_label",
+	    "vdev_path");
+	return (0);
+}
+
+static int
+spa_mmp_history_data(char *buf, size_t size, void *data)
+{
+	spa_mmp_history_t *smh = (spa_mmp_history_t *)data;
+
+	(void) snprintf(buf, size, "%-10llu %-10llu %-12llu %-24llu %-10llu "
+	    "%s\n",
+	    (u_longlong_t)smh->txg, (u_longlong_t)smh->timestamp,
+	    (u_longlong_t)smh->mmp_delay, (u_longlong_t)smh->vdev_guid,
+	    (u_longlong_t)smh->vdev_label,
+	    (smh->vdev_path ? smh->vdev_path : "-"));
+
+	return (0);
+}
+
+/*
+ * Calculate the address for the next spa_stats_history_t entry.  The
+ * ssh->lock will be held until ksp->ks_ndata entries are processed.
+ */
+static void *
+spa_mmp_history_addr(kstat_t *ksp, loff_t n)
+{
+	spa_t *spa = ksp->ks_private;
+	spa_stats_history_t *ssh = &spa->spa_stats.mmp_history;
+
+	ASSERT(MUTEX_HELD(&ssh->lock));
+
+	if (n == 0)
+		ssh->private = list_tail(&ssh->list);
+	else if (ssh->private)
+		ssh->private = list_prev(&ssh->list, ssh->private);
+
+	return (ssh->private);
+}
+
+/*
+ * When the kstat is written discard all spa_mmp_history_t entries.  The
+ * ssh->lock will be held until ksp->ks_ndata entries are processed.
+ */
+static int
+spa_mmp_history_update(kstat_t *ksp, int rw)
+{
+	spa_t *spa = ksp->ks_private;
+	spa_stats_history_t *ssh = &spa->spa_stats.mmp_history;
+
+	ASSERT(MUTEX_HELD(&ssh->lock));
+
+	if (rw == KSTAT_WRITE) {
+		spa_mmp_history_t *smh;
+
+		while ((smh = list_remove_head(&ssh->list))) {
+			ssh->size--;
+			if (smh->vdev_path)
+				strfree(smh->vdev_path);
+			kmem_free(smh, sizeof (spa_mmp_history_t));
+		}
+
+		ASSERT3U(ssh->size, ==, 0);
+	}
+
+	ksp->ks_ndata = ssh->size;
+	ksp->ks_data_size = ssh->size * sizeof (spa_mmp_history_t);
+
+	return (0);
+}
+
+static void
+spa_mmp_history_init(spa_t *spa)
+{
+	spa_stats_history_t *ssh = &spa->spa_stats.mmp_history;
+	char name[KSTAT_STRLEN];
+	kstat_t *ksp;
+
+	mutex_init(&ssh->lock, NULL, MUTEX_DEFAULT, NULL);
+	list_create(&ssh->list, sizeof (spa_mmp_history_t),
+	    offsetof(spa_mmp_history_t, smh_link));
+
+	ssh->count = 0;
+	ssh->size = 0;
+	ssh->private = NULL;
+
+	(void) snprintf(name, KSTAT_STRLEN, "zfs/%s", spa_name(spa));
+
+	ksp = kstat_create(name, 0, "multihost", "misc",
+	    KSTAT_TYPE_RAW, 0, KSTAT_FLAG_VIRTUAL);
+	ssh->kstat = ksp;
+
+	if (ksp) {
+		ksp->ks_lock = &ssh->lock;
+		ksp->ks_data = NULL;
+		ksp->ks_private = spa;
+		ksp->ks_update = spa_mmp_history_update;
+		kstat_set_raw_ops(ksp, spa_mmp_history_headers,
+		    spa_mmp_history_data, spa_mmp_history_addr);
+		kstat_install(ksp);
+	}
+}
+
+static void
+spa_mmp_history_destroy(spa_t *spa)
+{
+	spa_stats_history_t *ssh = &spa->spa_stats.mmp_history;
+	spa_mmp_history_t *smh;
+	kstat_t *ksp;
+
+	ksp = ssh->kstat;
+	if (ksp)
+		kstat_delete(ksp);
+
+	mutex_enter(&ssh->lock);
+	while ((smh = list_remove_head(&ssh->list))) {
+		ssh->size--;
+		if (smh->vdev_path)
+			strfree(smh->vdev_path);
+		kmem_free(smh, sizeof (spa_mmp_history_t));
+	}
+
+	ASSERT3U(ssh->size, ==, 0);
+	list_destroy(&ssh->list);
+	mutex_exit(&ssh->lock);
+
+	mutex_destroy(&ssh->lock);
+}
+
+/*
+ * Add a new MMP update to historical record.
+ */
+void
+spa_mmp_history_add(uint64_t txg, uint64_t timestamp, uint64_t mmp_delay,
+    vdev_t *vd, int label)
+{
+	spa_t *spa = vd->vdev_spa;
+	spa_stats_history_t *ssh = &spa->spa_stats.mmp_history;
+	spa_mmp_history_t *smh, *rm;
+
+	if (zfs_multihost_history == 0 && ssh->size == 0)
+		return;
+
+	smh = kmem_zalloc(sizeof (spa_mmp_history_t), KM_SLEEP);
+	smh->txg = txg;
+	smh->timestamp = timestamp;
+	smh->mmp_delay = mmp_delay;
+	smh->vdev_guid = vd->vdev_guid;
+	if (vd->vdev_path)
+		smh->vdev_path = strdup(vd->vdev_path);
+	smh->vdev_label = label;
+
+	mutex_enter(&ssh->lock);
+
+	list_insert_head(&ssh->list, smh);
+	ssh->size++;
+
+	while (ssh->size > zfs_multihost_history) {
+		ssh->size--;
+		rm = list_remove_tail(&ssh->list);
+		if (rm->vdev_path)
+			strfree(rm->vdev_path);
+		kmem_free(rm, sizeof (spa_mmp_history_t));
+	}
+
+	mutex_exit(&ssh->lock);
+}
+
 void
 spa_stats_init(spa_t *spa)
 {
@@ -708,6 +906,7 @@ spa_stats_init(spa_t *spa)
 	spa_txg_history_init(spa);
 	spa_tx_assign_init(spa);
 	spa_io_history_init(spa);
+	spa_mmp_history_init(spa);
 }
 
 void
@@ -717,15 +916,25 @@ spa_stats_destroy(spa_t *spa)
 	spa_txg_history_destroy(spa);
 	spa_read_history_destroy(spa);
 	spa_io_history_destroy(spa);
+	spa_mmp_history_destroy(spa);
 }
 
 #if defined(_KERNEL) && defined(HAVE_SPL)
+/* CSTYLED */
 module_param(zfs_read_history, int, 0644);
-MODULE_PARM_DESC(zfs_read_history, "Historic statistics for the last N reads");
+MODULE_PARM_DESC(zfs_read_history,
+	"Historical statistics for the last N reads");
 
 module_param(zfs_read_history_hits, int, 0644);
-MODULE_PARM_DESC(zfs_read_history_hits, "Include cache hits in read history");
+MODULE_PARM_DESC(zfs_read_history_hits,
+	"Include cache hits in read history");
 
 module_param(zfs_txg_history, int, 0644);
-MODULE_PARM_DESC(zfs_txg_history, "Historic statistics for the last N txgs");
+MODULE_PARM_DESC(zfs_txg_history,
+	"Historical statistics for the last N txgs");
+
+module_param(zfs_multihost_history, int, 0644);
+MODULE_PARM_DESC(zfs_multihost_history,
+	"Historical statistics for last N multihost writes");
+/* END CSTYLED */
 #endif
diff --git a/module/zfs/uberblock.c b/module/zfs/uberblock.c
index f8bdecdf5749..c1e85bdce760 100644
--- a/module/zfs/uberblock.c
+++ b/module/zfs/uberblock.c
@@ -44,7 +44,7 @@ uberblock_verify(uberblock_t *ub)
  * transaction group.
  */
 boolean_t
-uberblock_update(uberblock_t *ub, vdev_t *rvd, uint64_t txg)
+uberblock_update(uberblock_t *ub, vdev_t *rvd, uint64_t txg, uint64_t mmp_delay)
 {
 	ASSERT(ub->ub_txg < txg);
 
@@ -57,6 +57,9 @@ uberblock_update(uberblock_t *ub, vdev_t *rvd, uint64_t txg)
 	ub->ub_guid_sum = rvd->vdev_guid_sum;
 	ub->ub_timestamp = gethrestime_sec();
 	ub->ub_software_version = SPA_VERSION;
+	ub->ub_mmp_magic = MMP_MAGIC;
+	ub->ub_mmp_delay = spa_multihost(rvd->vdev_spa) ? mmp_delay : 0;
+	ub->ub_mmp_seq = 0;
 
 	return (ub->ub_rootbp.blk_birth == txg);
 }
diff --git a/module/zfs/vdev_label.c b/module/zfs/vdev_label.c
index 021f4774b5d7..a0a02366e1d9 100644
--- a/module/zfs/vdev_label.c
+++ b/module/zfs/vdev_label.c
@@ -193,7 +193,7 @@ vdev_label_read(zio_t *zio, vdev_t *vd, int l, abd_t *buf, uint64_t offset,
 	    ZIO_PRIORITY_SYNC_READ, flags, B_TRUE));
 }
 
-static void
+void
 vdev_label_write(zio_t *zio, vdev_t *vd, int l, abd_t *buf, uint64_t offset,
     uint64_t size, zio_done_func_t *done, void *private, int flags)
 {
@@ -1082,14 +1082,12 @@ static void
 vdev_uberblock_load_impl(zio_t *zio, vdev_t *vd, int flags,
     struct ubl_cbdata *cbp)
 {
-	int c, l, n;
-
-	for (c = 0; c < vd->vdev_children; c++)
+	for (int c = 0; c < vd->vdev_children; c++)
 		vdev_uberblock_load_impl(zio, vd->vdev_child[c], flags, cbp);
 
 	if (vd->vdev_ops->vdev_op_leaf && vdev_readable(vd)) {
-		for (l = 0; l < VDEV_LABELS; l++) {
-			for (n = 0; n < VDEV_UBERBLOCK_COUNT(vd); n++) {
+		for (int l = 0; l < VDEV_LABELS; l++) {
+			for (int n = 0; n < VDEV_UBERBLOCK_COUNT(vd); n++) {
 				vdev_label_read(zio, vd, l,
 				    abd_alloc_linear(VDEV_UBERBLOCK_SIZE(vd),
 				    B_TRUE), VDEV_UBERBLOCK_OFFSET(vd, n),
@@ -1213,10 +1211,7 @@ vdev_uberblock_sync_done(zio_t *zio)
 static void
 vdev_uberblock_sync(zio_t *zio, uberblock_t *ub, vdev_t *vd, int flags)
 {
-	abd_t *ub_abd;
-	int c, l, n;
-
-	for (c = 0; c < vd->vdev_children; c++)
+	for (int c = 0; c < vd->vdev_children; c++)
 		vdev_uberblock_sync(zio, ub, vd->vdev_child[c], flags);
 
 	if (!vd->vdev_ops->vdev_op_leaf)
@@ -1232,14 +1227,15 @@ vdev_uberblock_sync(zio_t *zio, uberblock_t *ub, vdev_t *vd, int flags)
 		vd->vdev_copy_uberblocks = B_FALSE;
 	}
 
-	n = ub->ub_txg & (VDEV_UBERBLOCK_COUNT(vd) - 1);
+	int m = spa_multihost(vd->vdev_spa) ? MMP_BLOCKS_PER_LABEL : 0;
+	int n = ub->ub_txg % (VDEV_UBERBLOCK_COUNT(vd) - m);
 
 	/* Copy the uberblock_t into the ABD */
-	ub_abd = abd_alloc_for_io(VDEV_UBERBLOCK_SIZE(vd), B_TRUE);
+	abd_t *ub_abd = abd_alloc_for_io(VDEV_UBERBLOCK_SIZE(vd), B_TRUE);
 	abd_zero(ub_abd, VDEV_UBERBLOCK_SIZE(vd));
 	abd_copy_from_buf(ub_abd, ub, sizeof (uberblock_t));
 
-	for (l = 0; l < VDEV_LABELS; l++)
+	for (int l = 0; l < VDEV_LABELS; l++)
 		vdev_label_write(zio, vd, l, ub_abd,
 		    VDEV_UBERBLOCK_OFFSET(vd, n), VDEV_UBERBLOCK_SIZE(vd),
 		    vdev_uberblock_sync_done, zio->io_private,
@@ -1448,10 +1444,13 @@ vdev_config_sync(vdev_t **svd, int svdcount, uint64_t txg)
 	 * and the vdev configuration hasn't changed,
 	 * then there's nothing to do.
 	 */
-	if (ub->ub_txg < txg &&
-	    uberblock_update(ub, spa->spa_root_vdev, txg) == B_FALSE &&
-	    list_is_empty(&spa->spa_config_dirty_list))
-		return (0);
+	if (ub->ub_txg < txg) {
+		boolean_t changed = uberblock_update(ub, spa->spa_root_vdev,
+		    txg, spa->spa_mmp.mmp_delay);
+
+		if (!changed && list_is_empty(&spa->spa_config_dirty_list))
+			return (0);
+	}
 
 	if (txg > spa_freeze_txg(spa))
 		return (0);
@@ -1502,6 +1501,10 @@ vdev_config_sync(vdev_t **svd, int svdcount, uint64_t txg)
 	if ((error = vdev_uberblock_sync_list(svd, svdcount, ub, flags)) != 0)
 		goto retry;
 
+
+	if (spa_multihost(spa))
+		mmp_update_uberblock(spa, ub);
+
 	/*
 	 * Sync out odd labels for every dirty vdev.  If the system dies
 	 * in the middle of this process, the even labels and the new
diff --git a/module/zfs/zfs_ioctl.c b/module/zfs/zfs_ioctl.c
index 728b023773e4..b2f5db584daa 100644
--- a/module/zfs/zfs_ioctl.c
+++ b/module/zfs/zfs_ioctl.c
@@ -1650,7 +1650,7 @@ zfs_ioc_pool_stats(zfs_cmd_t *zc)
 static int
 zfs_ioc_pool_tryimport(zfs_cmd_t *zc)
 {
-	nvlist_t *tryconfig, *config;
+	nvlist_t *tryconfig, *config = NULL;
 	int error;
 
 	if ((error = get_nvlist(zc->zc_nvlist_conf, zc->zc_nvlist_conf_size,
diff --git a/scripts/zfs-tests.sh b/scripts/zfs-tests.sh
index c4db08d78ca6..eb2ce38288f5 100755
--- a/scripts/zfs-tests.sh
+++ b/scripts/zfs-tests.sh
@@ -43,7 +43,8 @@ SINGLETEST=()
 SINGLETESTUSER="root"
 ZFS_DBGMSG="$STF_SUITE/callbacks/zfs_dbgmsg.ksh"
 ZFS_DMESG="$STF_SUITE/callbacks/zfs_dmesg.ksh"
-TESTFAIL_CALLBACKS=${TESTFAIL_CALLBACKS:-"$ZFS_DBGMSG:$ZFS_DMESG"}
+ZFS_MMP="$STF_SUITE/callbacks/zfs_mmp.ksh"
+TESTFAIL_CALLBACKS=${TESTFAIL_CALLBACKS:-"$ZFS_DBGMSG:$ZFS_DMESG:$ZFS_MMP"}
 
 #
 # Attempt to remove loopback devices and files which where created earlier
diff --git a/tests/runfiles/linux.run b/tests/runfiles/linux.run
index 9f195628c2e8..e556f1e8cc1d 100644
--- a/tests/runfiles/linux.run
+++ b/tests/runfiles/linux.run
@@ -410,6 +410,10 @@ tests = ['migration_001_pos', 'migration_002_pos', 'migration_003_pos',
 [tests/functional/mmap]
 tests = ['mmap_write_001_pos', 'mmap_read_001_pos']
 
+[tests/functional/mmp]
+tests = ['mmp_on_thread', 'mmp_on_uberblocks', 'mmp_on_off', 'mmp_interval',
+    'mmp_active_import', 'mmp_inactive_import', 'mmp_exported_import']
+
 [tests/functional/mount]
 tests = ['umount_001', 'umountall_001']
 
diff --git a/tests/zfs-tests/callbacks/Makefile.am b/tests/zfs-tests/callbacks/Makefile.am
index 71947f3084ea..30e847241167 100644
--- a/tests/zfs-tests/callbacks/Makefile.am
+++ b/tests/zfs-tests/callbacks/Makefile.am
@@ -1,4 +1,5 @@
 pkgdatadir = $(datadir)/@PACKAGE@/zfs-tests/callbacks
 dist_pkgdata_SCRIPTS = \
 	zfs_dbgmsg.ksh \
-	zfs_dmesg.ksh
+	zfs_dmesg.ksh \
+	zfs_mmp.ksh
diff --git a/tests/zfs-tests/callbacks/zfs_mmp.ksh b/tests/zfs-tests/callbacks/zfs_mmp.ksh
new file mode 100755
index 000000000000..df2cd132d31a
--- /dev/null
+++ b/tests/zfs-tests/callbacks/zfs_mmp.ksh
@@ -0,0 +1,37 @@
+#!/bin/ksh -p
+
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+
+#
+# Copyright (c) 2017 by Lawrence Livermore National Security.
+# All rights reserved.
+#
+
+# $1: number of lines to output (default: 40)
+typeset lines=${1:-40}
+typeset history=$(cat /sys/module/zfs/parameters/zfs_multihost_history)
+
+if [ $history -eq 0 ]; then
+	exit
+fi
+
+for f in /proc/spl/kstat/zfs/*/multihost; do
+	echo "================================================================="
+	echo " Last $lines lines of $f"
+	echo "================================================================="
+
+	sudo tail -n $lines $f
+done
+
+echo "================================================================="
+echo " End of zfs multihost log"
+echo "================================================================="
diff --git a/tests/zfs-tests/include/commands.cfg b/tests/zfs-tests/include/commands.cfg
index 968ab3cd1a5b..57b1bd3158ad 100644
--- a/tests/zfs-tests/include/commands.cfg
+++ b/tests/zfs-tests/include/commands.cfg
@@ -52,6 +52,7 @@ export SYSTEM_FILES='arp
     gunzip
     gzip
     head
+    hostid
     hostname
     id
     iostat
diff --git a/tests/zfs-tests/include/libtest.shlib b/tests/zfs-tests/include/libtest.shlib
index ddfe550bff23..1d1c57e7a4cf 100644
--- a/tests/zfs-tests/include/libtest.shlib
+++ b/tests/zfs-tests/include/libtest.shlib
@@ -3428,3 +3428,83 @@ function swap_cleanup
 
 	return 0
 }
+
+#
+# Set a global system tunable (64-bit value)
+#
+# $1 tunable name
+# $2 tunable values
+#
+function set_tunable64
+{
+	set_tunable_impl "$1" "$2" Z
+}
+
+#
+# Set a global system tunable (32-bit value)
+#
+# $1 tunable name
+# $2 tunable values
+#
+function set_tunable32
+{
+	set_tunable_impl "$1" "$2" W
+}
+
+function set_tunable_impl
+{
+	typeset tunable="$1"
+	typeset value="$2"
+	typeset mdb_cmd="$3"
+	typeset module="${4:-zfs}"
+
+	[[ -z "$tunable" ]] && return 1
+	[[ -z "$value" ]] && return 1
+	[[ -z "$mdb_cmd" ]] && return 1
+
+	case "$(uname)" in
+	Linux)
+		typeset zfs_tunables="/sys/module/$module/parameters"
+		[[ -w "$zfs_tunables/$tunable" ]] || return 1
+		echo -n "$value" > "$zfs_tunables/$tunable"
+		return "$?"
+		;;
+	SunOS)
+		[[ "$module" -eq "zfs" ]] || return 1
+		echo "${tunable}/${mdb_cmd}0t${value}" | mdb -kw
+		return "$?"
+		;;
+	esac
+}
+
+#
+# Get a global system tunable
+#
+# $1 tunable name
+#
+function get_tunable
+{
+	get_tunable_impl "$1"
+}
+
+function get_tunable_impl
+{
+	typeset tunable="$1"
+	typeset module="${2:-zfs}"
+
+	[[ -z "$tunable" ]] && return 1
+
+	case "$(uname)" in
+	Linux)
+		typeset zfs_tunables="/sys/module/$module/parameters"
+		[[ -f "$zfs_tunables/$tunable" ]] || return 1
+		cat $zfs_tunables/$tunable
+		return "$?"
+		;;
+	SunOS)
+		[[ "$module" -eq "zfs" ]] || return 1
+		;;
+	esac
+
+	return 1
+}
diff --git a/tests/zfs-tests/tests/functional/Makefile.am b/tests/zfs-tests/tests/functional/Makefile.am
index 1c3f4b1a877b..d68f254ef275 100644
--- a/tests/zfs-tests/tests/functional/Makefile.am
+++ b/tests/zfs-tests/tests/functional/Makefile.am
@@ -29,6 +29,7 @@ SUBDIRS = \
 	link_count \
 	migration \
 	mmap \
+	mmp \
 	mount \
 	mv_files \
 	nestedfs \
diff --git a/tests/zfs-tests/tests/functional/cli_root/zpool_get/zpool_get.cfg b/tests/zfs-tests/tests/functional/cli_root/zpool_get/zpool_get.cfg
index 0ffd6f510818..e1537806f297 100644
--- a/tests/zfs-tests/tests/functional/cli_root/zpool_get/zpool_get.cfg
+++ b/tests/zfs-tests/tests/functional/cli_root/zpool_get/zpool_get.cfg
@@ -54,6 +54,7 @@ typeset -a properties=(
     "freeing"
     "fragmentation"
     "leaked"
+    "multihost"
     "feature@async_destroy"
     "feature@empty_bpobj"
     "feature@lz4_compress"
diff --git a/tests/zfs-tests/tests/functional/mmp/Makefile.am b/tests/zfs-tests/tests/functional/mmp/Makefile.am
new file mode 100644
index 000000000000..2399a6c377d2
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/mmp/Makefile.am
@@ -0,0 +1,13 @@
+pkgdatadir = $(datadir)/@PACKAGE@/zfs-tests/tests/functional/mmp
+dist_pkgdata_SCRIPTS = \
+	mmp_on_thread.ksh \
+	mmp_on_uberblocks.ksh \
+	mmp_on_off.ksh \
+	mmp_interval.ksh \
+	mmp_active_import.ksh \
+	mmp_inactive_import.ksh \
+	mmp_exported_import.ksh \
+	setup.ksh \
+	cleanup.ksh \
+	mmp.kshlib \
+	mmp.cfg
diff --git a/tests/zfs-tests/tests/functional/mmp/cleanup.ksh b/tests/zfs-tests/tests/functional/mmp/cleanup.ksh
new file mode 100755
index 000000000000..6e438d88dbc2
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/mmp/cleanup.ksh
@@ -0,0 +1,28 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+# CDDL HEADER END
+#
+
+#
+# Copyright (c) 2017 by Lawrence Livermore National Security, LLC.
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/tests/functional/mmp/mmp.cfg
+
+verify_runnable "global"
+
+log_must set_tunable64 zfs_multihost_history 0
+
+log_pass "mmp cleanup passed"
diff --git a/tests/zfs-tests/tests/functional/mmp/mmp.cfg b/tests/zfs-tests/tests/functional/mmp/mmp.cfg
new file mode 100644
index 000000000000..f17108a87630
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/mmp/mmp.cfg
@@ -0,0 +1,38 @@
+#
+# CDDL HEADER START
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+# CDDL HEADER END
+#
+
+#
+# Copyright (c) 2017 by Lawrence Livermore National Security, LLC.
+#
+
+export PREV_UBER="$TEST_BASE_DIR/mmp-uber-prev.txt"
+export CURR_UBER="$TEST_BASE_DIR/mmp-uber-curr.txt"
+export DISK=${DISKS%% *}
+
+export HOSTID_FILE="/etc/hostid"
+export HOSTID1=01234567
+export HOSTID2=89abcdef
+
+export TXG_TIMEOUT_LONG=5000
+export TXG_TIMEOUT_DEFAULT=5
+
+export MMP_POOL=mmppool
+export MMP_DIR=$TEST_BASE_DIR/mmp
+export MMP_HISTORY=100
+
+export MMP_INTERVAL_DEFAULT=1000
+export MMP_INTERVAL_MIN=100
+
+export ZPOOL_IMPORT_DURATION=9
diff --git a/tests/zfs-tests/tests/functional/mmp/mmp.kshlib b/tests/zfs-tests/tests/functional/mmp/mmp.kshlib
new file mode 100644
index 000000000000..a81779b0c7fb
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/mmp/mmp.kshlib
@@ -0,0 +1,186 @@
+#
+# CDDL HEADER START
+#
+# The contents of this file are subject to the terms of the
+# Common Development and Distribution License (the "License").
+# You may not use this file except in compliance with the License.
+#
+# You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+# or http://www.opensolaris.org/os/licensing.
+# See the License for the specific language governing permissions
+# and limitations under the License.
+#
+# When distributing Covered Code, include this CDDL HEADER in each
+# file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+# If applicable, add the following below this CDDL HEADER, with the
+# fields enclosed by brackets "[]" replaced with your own identifying
+# information: Portions Copyright [yyyy] [name of copyright owner]
+#
+# CDDL HEADER END
+#
+
+#
+# Copyright (c) 2017 by Lawrence Livermore National Security, LLC.
+# Use is subject to license terms.
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/tests/functional/mmp/mmp.cfg
+
+
+function check_pool_import # pool opts token keyword
+{
+	typeset pool=${1:-$MMP_POOL}
+	typeset opts=$2
+	typeset token=$3
+	typeset keyword=$4
+
+	zpool import $opts 2>&1 | \
+	    nawk -v token="$token:" '($1==token) {print $0}' | \
+	    grep -i "$keyword" > /dev/null 2>&1
+
+	return $?
+}
+
+function is_pool_imported # pool opts
+{
+	typeset pool=${1:-$MMP_POOL}
+	typeset opts=$2
+
+	check_pool_import "$pool" "$opts" "status" \
+	    "The pool is currently imported"
+	return $?
+}
+
+function wait_pool_imported # pool opts
+{
+	typeset pool=${1:-$MMP_POOL}
+	typeset opts=$2
+
+	while is_pool_imported "$pool" "$opts"; do
+		log_must sleep 5
+	done
+
+	return 0
+}
+
+function try_pool_import # pool opts message
+{
+	typeset pool=${1:-$MMP_POOL}
+	typeset opts=$2
+	typeset msg=$3
+
+	zpool import $opts $pool 2>&1 | grep -i "$msg"
+
+	return $?
+}
+
+function mmp_set_hostid
+{
+	typeset hostid=$1
+
+	a=${hostid:6:2}
+	b=${hostid:4:2}
+	c=${hostid:2:2}
+	d=${hostid:0:2}
+
+	printf "\\x$a\\x$b\\x$c\\x$d" >$HOSTID_FILE
+
+	if [ $(hostid) != "$hostid" ]; then
+		return 1
+	fi
+
+	return 0
+}
+
+function mmp_clear_hostid
+{
+	rm -f $HOSTID_FILE
+}
+
+function mmp_pool_create # pool dir
+{
+	typeset pool=${1:-$MMP_POOL}
+	typeset dir=${2:-$MMP_DIR}
+	typeset opts="-T120 -M -k0 -f $dir -E -p $pool"
+
+	log_must mkdir -p $dir
+	log_must truncate -s $MINVDEVSIZE $dir/vdev1 $dir/vdev2
+
+	log_must mmp_set_hostid $HOSTID1
+	log_must zpool create -f $pool mirror $dir/vdev1 $dir/vdev2
+	log_must zpool set multihost=on $pool
+	log_must zpool export $pool
+	log_must mmp_set_hostid $HOSTID2
+
+	log_note "Starting ztest in the background as hostid $HOSTID1"
+	log_must eval "ZFS_HOSTID=$HOSTID1 ztest $opts >/dev/null 2>&1 &"
+
+	while ! is_pool_imported "$pool" "-d $dir"; do
+		log_must pgrep ztest
+		log_must sleep 5
+	done
+}
+
+function mmp_pool_destroy # pool dir
+{
+	typeset pool=${1:-$MMP_POOL}
+	typeset dir=${2:-$MMP_DIR}
+
+	ZTESTPID=$(pgrep ztest)
+	if [ -n "$ZTESTPID" ]; then
+		log_must kill $ZTESTPID
+		wait $ZTESTPID
+	fi
+
+	if poolexists $pool; then
+		destroy_pool $pool
+        fi
+
+	rm -Rf $dir
+	mmp_clear_hostid
+}
+
+function mmp_pool_set_hostid # pool hostid
+{
+	typeset pool=$1
+	typeset hostid=$2
+
+	log_must mmp_set_hostid $hostid
+	log_must zpool export $pool
+	log_must zpool import $pool
+
+	return 0
+}
+
+function import_no_activity_check # pool opts
+{
+	typeset pool=$1
+	typeset opts=$2
+
+	SECONDS=0
+	zpool import $opts $pool
+	typeset rc=$?
+
+	if [[ $SECONDS -gt $ZPOOL_IMPORT_DURATION ]]; then
+		log_fail "unexpected activity check (${SECONDS}s)"
+	fi
+
+	return $rc
+}
+
+function import_activity_check # pool opts
+{
+	typeset pool=$1
+	typeset opts=$2
+
+	SECONDS=0
+	zpool import $opts $pool
+	typeset rc=$?
+
+	if [[ $SECONDS -le $ZPOOL_IMPORT_DURATION ]]; then
+		log_fail "expected activity check (${SECONDS}s)"
+	fi
+
+	return $rc
+}
diff --git a/tests/zfs-tests/tests/functional/mmp/mmp_active_import.ksh b/tests/zfs-tests/tests/functional/mmp/mmp_active_import.ksh
new file mode 100755
index 000000000000..92eb9ce2d229
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/mmp/mmp_active_import.ksh
@@ -0,0 +1,104 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+# CDDL HEADER END
+#
+
+#
+# Copyright (c) 2017 by Lawrence Livermore National Security, LLC.
+#
+
+# DESCRIPTION:
+#	Under no circumstances when multihost is active, should an active pool
+#	with one hostid be importable by a host with a different hostid.
+#
+# STRATEGY:
+#	 1. Simulate an active pool on another host with ztest.
+#	 2. Verify 'zpool import' reports an active pool.
+#	 3. Verify 'zpool import [-f] $MMP_POOL' cannot import the pool.
+#	 4. Kill ztest to make pool eligible for import.
+#	 5. Verify 'zpool import' fails with the expected error message.
+#	 6. Verify 'zpool import $MMP_POOL' fails with the expected message.
+#	 7. Verify 'zpool import -f $MMP_POOL' can now import the pool.
+#	 8. Verify pool may be exported/imported without -f argument.
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/tests/functional/mmp/mmp.cfg
+. $STF_SUITE/tests/functional/mmp/mmp.kshlib
+
+verify_runnable "both"
+
+function cleanup
+{
+	mmp_pool_destroy $MMP_DIR $MMP_POOL
+	log_must set_tunable64 zfs_multihost_interval $MMP_INTERVAL_DEFAULT
+	log_must mmp_clear_hostid
+}
+
+log_assert "multihost=on|off active pool activity checks"
+log_onexit cleanup
+
+# 1. Simulate an active pool on another host with ztest.
+mmp_pool_destroy $MMP_POOL $MMP_DIR
+mmp_pool_create $MMP_POOL $MMP_DIR
+
+# 2. Verify 'zpool import' reports an active pool.
+log_must mmp_set_hostid $HOSTID2
+log_must set_tunable64 zfs_multihost_interval $MMP_INTERVAL_MIN
+log_must is_pool_imported $MMP_POOL "-d $MMP_DIR"
+
+# 3. Verify 'zpool import [-f] $MMP_POOL' cannot import the pool.
+MMP_IMPORTED_MSG="Cannot import '$MMP_POOL': pool is imported"
+log_must try_pool_import $MMP_POOL "-d $MMP_DIR" $MMP_IMPORTED_MSG
+for i in {1..10}; do
+	log_must pgrep ztest >/dev/null
+	log_must try_pool_import $MMP_POOL "-f -d $MMP_DIR" $MMP_IMPORTED_MSG
+done
+
+# 4. Kill ztest to make pool eligible for import.  Poll with 'zpool status'.
+ZTESTPID=$(pgrep ztest)
+if [ -n "$ZTESTPID" ]; then
+	log_must kill -9 $ZTESTPID
+fi
+log_must wait_pool_imported $MMP_POOL "-d $MMP_DIR"
+
+# 5. Verify 'zpool import' fails with the expected error message, when
+#    - hostid=0:        - configuration error
+#    - hostid=matches   - safe to import the pool
+#    - hostid=different - previously imported on a different system
+#
+log_must mmp_clear_hostid
+MMP_IMPORTED_MSG="Set the system hostid"
+log_must check_pool_import $MMP_POOL "-d $MMP_DIR" "action" $MMP_IMPORTED_MSG
+
+log_must mmp_set_hostid $HOSTID1
+MMP_IMPORTED_MSG="The pool can be imported"
+log_must check_pool_import $MMP_POOL "-d $MMP_DIR" "action" $MMP_IMPORTED_MSG
+
+log_must mmp_set_hostid $HOSTID2
+MMP_IMPORTED_MSG="The pool was last accessed by another system."
+log_must check_pool_import $MMP_POOL "-d $MMP_DIR" "status" $MMP_IMPORTED_MSG
+
+# 6. Verify 'zpool import $MMP_POOL' fails with the expected message.
+MMP_IMPORTED_MSG="pool was previously in use from another system."
+log_must try_pool_import $MMP_POOL "-d $MMP_DIR" $MMP_IMPORTED_MSG
+
+# 7. Verify 'zpool import -f $MMP_POOL' can now import the pool.
+log_must import_activity_check $MMP_POOL "-f -d $MMP_DIR"
+
+# 8 Verify pool may be exported/imported without -f argument.
+log_must zpool export $MMP_POOL
+log_must import_no_activity_check $MMP_POOL "-d $MMP_DIR"
+
+log_pass "multihost=on|off active pool activity checks passed"
diff --git a/tests/zfs-tests/tests/functional/mmp/mmp_exported_import.ksh b/tests/zfs-tests/tests/functional/mmp/mmp_exported_import.ksh
new file mode 100755
index 000000000000..d65ca5b3d764
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/mmp/mmp_exported_import.ksh
@@ -0,0 +1,104 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+# CDDL HEADER END
+#
+
+#
+# Copyright (c) 2017 by Lawrence Livermore National Security, LLC.
+#
+
+# DESCRIPTION:
+#	Verify import behavior for exported pool (no activity check)
+#
+# STRATEGY:
+#	1. Create a zpool
+#	2. Verify multihost=off and hostids match (no activity check)
+#	3. Verify multihost=off and hostids differ (no activity check)
+#	4. Verify multihost=off and hostid zero allowed (no activity check)
+#	5. Verify multihost=on and hostids match (no activity check)
+#	6. Verify multihost=on and hostids differ (no activity check)
+#	7. Verify multihost=on and hostid zero fails (no activity check)
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/tests/functional/mmp/mmp.cfg
+. $STF_SUITE/tests/functional/mmp/mmp.kshlib
+
+verify_runnable "both"
+
+function cleanup
+{
+	default_cleanup_noexit
+	log_must mmp_clear_hostid
+}
+
+log_assert "multihost=on|off activity checks exported pool"
+log_onexit cleanup
+
+# 1. Create a zpool
+log_must mmp_set_hostid $HOSTID1
+default_setup_noexit $DISK
+
+# 2. Verify multihost=off and hostids match (no activity check)
+log_must zpool set multihost=off $TESTPOOL
+
+for opt in "" "-f"; do
+	log_must zpool export $TESTPOOL
+	log_must import_no_activity_check $TESTPOOL $opt
+done
+
+# 3. Verify multihost=off and hostids differ (no activity check)
+for opt in "" "-f"; do
+	log_must mmp_pool_set_hostid $TESTPOOL $HOSTID1
+	log_must zpool export $TESTPOOL
+	log_must mmp_set_hostid $HOSTID2
+	log_must import_no_activity_check $TESTPOOL $opt
+done
+
+# 4. Verify multihost=off and hostid zero allowed (no activity check)
+log_must mmp_clear_hostid
+
+for opt in "" "-f"; do
+	log_must zpool export $TESTPOOL
+	log_must import_no_activity_check $TESTPOOL $opt
+done
+
+# 5. Verify multihost=on and hostids match (no activity check)
+log_must mmp_pool_set_hostid $TESTPOOL $HOSTID1
+log_must zpool set multihost=on $TESTPOOL
+
+for opt in "" "-f"; do
+	log_must zpool export $TESTPOOL
+	log_must import_no_activity_check $TESTPOOL $opt
+done
+
+# 6. Verify multihost=on and hostids differ (no activity check)
+for opt in "" "-f"; do
+	log_must mmp_pool_set_hostid $TESTPOOL $HOSTID1
+	log_must zpool export $TESTPOOL
+	log_must mmp_set_hostid $HOSTID2
+	log_must import_no_activity_check $TESTPOOL $opt
+done
+
+# 7. Verify multihost=on and hostid zero fails (no activity check)
+log_must zpool export $TESTPOOL
+log_must mmp_clear_hostid
+
+for opt in "" "-f"; do
+	MMP_IMPORTED_MSG="Set the system hostid"
+	log_must check_pool_import $TESTPOOL "" "action" $MMP_IMPORTED_MSG
+	log_mustnot import_no_activity_check $TESTPOOL $opt
+done
+
+log_pass "multihost=on|off exported pool activity checks passed"
diff --git a/tests/zfs-tests/tests/functional/mmp/mmp_inactive_import.ksh b/tests/zfs-tests/tests/functional/mmp/mmp_inactive_import.ksh
new file mode 100755
index 000000000000..c944b6b2898b
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/mmp/mmp_inactive_import.ksh
@@ -0,0 +1,95 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+# CDDL HEADER END
+#
+
+#
+# Copyright (c) 2017 by Lawrence Livermore National Security, LLC.
+#
+
+# DESCRIPTION:
+#	Verify import behavior for inactive, but not exported, pools
+#
+# STRATEGY:
+#	1. Create a zpool
+#	2. Verify multihost=off and hostids match (no activity check)
+#	3. Verify multihost=off and hostids differ (no activity check)
+#	4. Verify multihost=off and hostid allowed (no activity check)
+#	5. Verify multihost=on and hostids match (no activity check)
+#	6. Verify multihost=on and hostids differ (activity check)
+#	7. Verify multihost=on and hostid zero fails (activity check)
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/tests/functional/mmp/mmp.cfg
+. $STF_SUITE/tests/functional/mmp/mmp.kshlib
+
+verify_runnable "both"
+
+function cleanup
+{
+	default_cleanup_noexit
+	log_must mmp_clear_hostid
+}
+
+log_assert "multihost=on|off inactive pool activity checks"
+log_onexit cleanup
+
+# 1. Create a zpool
+log_must mmp_set_hostid $HOSTID1
+default_setup_noexit $DISK
+
+# 2. Verify multihost=off and hostids match (no activity check)
+log_must zpool set multihost=off $TESTPOOL
+
+for opt in "" "-f"; do
+	log_must zpool export -F $TESTPOOL
+	log_must import_no_activity_check $TESTPOOL $opt
+done
+
+# 3. Verify multihost=off and hostids differ (no activity check)
+log_must zpool export -F $TESTPOOL
+log_must mmp_set_hostid $HOSTID2
+log_mustnot import_no_activity_check $TESTPOOL ""
+log_must import_no_activity_check $TESTPOOL "-f"
+
+# 4. Verify multihost=off and hostid zero allowed (no activity check)
+log_must zpool export -F $TESTPOOL
+log_must mmp_clear_hostid
+log_mustnot import_no_activity_check $TESTPOOL ""
+log_must import_no_activity_check $TESTPOOL "-f"
+
+# 5. Verify multihost=on and hostids match (no activity check)
+log_must mmp_pool_set_hostid $TESTPOOL $HOSTID1
+log_must zpool set multihost=on $TESTPOOL
+
+for opt in "" "-f"; do
+	log_must zpool export -F $TESTPOOL
+	log_must import_no_activity_check $TESTPOOL $opt
+done
+
+# 6. Verify multihost=on and hostids differ (activity check)
+log_must zpool export -F $TESTPOOL
+log_must mmp_set_hostid $HOSTID2
+log_mustnot import_activity_check $TESTPOOL ""
+log_must import_activity_check $TESTPOOL "-f"
+
+# 7. Verify multihost=on and hostid zero fails (activity check)
+log_must zpool export -F $TESTPOOL
+log_must mmp_clear_hostid
+MMP_IMPORTED_MSG="Set the system hostid"
+log_must check_pool_import $TESTPOOL "-f" "action" $MMP_IMPORTED_MSG
+log_mustnot import_activity_check $TESTPOOL "-f"
+
+log_pass "multihost=on|off inactive pool activity checks passed"
diff --git a/tests/zfs-tests/tests/functional/mmp/mmp_interval.ksh b/tests/zfs-tests/tests/functional/mmp/mmp_interval.ksh
new file mode 100755
index 000000000000..fb44d6191be6
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/mmp/mmp_interval.ksh
@@ -0,0 +1,47 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+# CDDL HEADER END
+#
+
+#
+# Copyright (c) 2017 by Lawrence Livermore National Security, LLC.
+#
+
+# DESCRIPTION:
+#	zfs_multihost_interval should only accept valid values.
+#
+# STRATEGY:
+#	1. Set zfs_multihost_interval to invalid values (negative).
+#	2. Set zfs_multihost_interval to valid values.
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/tests/functional/mmp/mmp.cfg
+. $STF_SUITE/tests/functional/mmp/mmp.kshlib
+
+verify_runnable "both"
+
+function cleanup
+{
+	log_must set_tunable64 zfs_multihost_interval $MMP_INTERVAL_DEFAULT
+}
+
+log_assert "zfs_multihost_interval cannot be set to an invalid value"
+log_onexit cleanup
+
+log_mustnot set_tunable64 zfs_multihost_interval -1
+log_must set_tunable64 zfs_multihost_interval $MMP_INTERVAL_MIN
+log_must set_tunable64 zfs_multihost_interval $MMP_INTERVAL_DEFAULT
+
+log_pass "zfs_multihost_interval cannot be set to an invalid value"
diff --git a/tests/zfs-tests/tests/functional/mmp/mmp_on_off.ksh b/tests/zfs-tests/tests/functional/mmp/mmp_on_off.ksh
new file mode 100755
index 000000000000..8bef86a0ffc1
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/mmp/mmp_on_off.ksh
@@ -0,0 +1,79 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+# CDDL HEADER END
+#
+
+#
+# Copyright (c) 2017 by Lawrence Livermore National Security, LLC.
+#
+
+# DESCRIPTION:
+#	When multihost=off ensure that leaf vdev uberblocks are not updated.
+#
+# STRATEGY:
+#	1. Set multihost=off (disables mmp)
+#	2. Set zfs_txg_timeout to large value
+#	3. Create a zpool
+#	4. Find the current "best" uberblock
+#	5. Sleep for enough time for uberblocks to change
+#	6. Find the current "best" uberblock
+#	7. If the uberblock changed, fail
+#	8. Set multihost=on
+#	9. Sleep for enough time for uberblocks to change
+#	10. Find the current "best" uberblock
+#	11. If uberblocks didn't change, fail
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/tests/functional/mmp/mmp.cfg
+. $STF_SUITE/tests/functional/mmp/mmp.kshlib
+
+verify_runnable "both"
+
+function cleanup
+{
+	default_cleanup_noexit
+	log_must set_tunable64 zfs_txg_timeout $TXG_TIMEOUT_DEFAULT
+	log_must set_tunable64 zfs_multihost_interval $MMP_INTERVAL_DEFAULT
+	log_must rm -f $PREV_UBER $CURR_UBER
+	log_must mmp_clear_hostid
+}
+
+log_assert "mmp thread won't write uberblocks with multihost=off"
+log_onexit cleanup
+
+log_must set_tunable64 zfs_multihost_interval $MMP_INTERVAL_MIN
+log_must set_tunable64 zfs_txg_timeout $TXG_TIMEOUT_LONG
+log_must mmp_set_hostid $HOSTID1
+
+default_setup_noexit $DISK
+log_must zpool set multihost=off $TESTPOOL
+
+log_must zdb -u $TESTPOOL > $PREV_UBER
+log_must sleep 5
+log_must zdb -u $TESTPOOL > $CURR_UBER
+
+if ! diff "$CURR_UBER" "$PREV_UBER"; then
+	log_fail "mmp thread has updated an uberblock"
+fi
+
+log_must zpool set multihost=on $TESTPOOL
+log_must sleep 5
+log_must zdb -u $TESTPOOL > $CURR_UBER
+
+if diff "$CURR_UBER" "$PREV_UBER"; then
+	log_fail "mmp failed to update uberblocks"
+fi
+
+log_pass "mmp thread won't write uberblocks with multihost=off passed"
diff --git a/tests/zfs-tests/tests/functional/mmp/mmp_on_thread.ksh b/tests/zfs-tests/tests/functional/mmp/mmp_on_thread.ksh
new file mode 100755
index 000000000000..07384c623167
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/mmp/mmp_on_thread.ksh
@@ -0,0 +1,64 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+# CDDL HEADER END
+#
+
+#
+# Copyright (c) 2017 by Lawrence Livermore National Security, LLC.
+#
+
+# DESCRIPTION:
+#	Ensure that the MMP thread is writing uberblocks.
+#
+# STRATEGY:
+#	1. Set zfs_txg_timeout to large value
+#	2. Create a zpool
+#	3. Find the current "best" uberblock
+#	4. Sleep for enough time for a potential uberblock update
+#	5. Find the current "best" uberblock
+#	6. If the uberblock never changed, fail
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/tests/functional/mmp/mmp.cfg
+. $STF_SUITE/tests/functional/mmp/mmp.kshlib
+
+verify_runnable "both"
+
+function cleanup
+{
+	default_cleanup_noexit
+	log_must set_tunable64 zfs_txg_timeout $TXG_TIMEOUT_DEFAULT
+	log_must rm -f $PREV_UBER $CURR_UBER
+	log_must mmp_clear_hostid
+}
+
+log_assert "mmp thread writes uberblocks (MMP)"
+log_onexit cleanup
+
+log_must set_tunable64 zfs_txg_timeout $TXG_TIMEOUT_LONG
+log_must mmp_set_hostid $HOSTID1
+
+default_setup_noexit $DISK
+log_must zpool set multihost=on $TESTPOOL
+
+log_must zdb -u $TESTPOOL > $PREV_UBER
+log_must sleep 5
+log_must zdb -u $TESTPOOL > $CURR_UBER
+
+if diff -u "$CURR_UBER" "$PREV_UBER"; then
+	log_fail "mmp failed to update uberblocks"
+fi
+
+log_pass "mmp thread writes uberblocks (MMP) passed"
diff --git a/tests/zfs-tests/tests/functional/mmp/mmp_on_uberblocks.ksh b/tests/zfs-tests/tests/functional/mmp/mmp_on_uberblocks.ksh
new file mode 100755
index 000000000000..2e21e2feff42
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/mmp/mmp_on_uberblocks.ksh
@@ -0,0 +1,79 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+# CDDL HEADER END
+#
+
+#
+# Copyright (c) 2017 by Lawrence Livermore National Security, LLC.
+#
+
+# DESCRIPTION:
+#	Ensure that MMP updates uberblocks at the expected intervals.
+#
+# STRATEGY:
+#	1. Set zfs_txg_timeout to large value
+#	2. Create a zpool
+#	3. Find the current "best" uberblock
+#	4. Loop for 10 seconds, increment counter for each change in UB
+#	5. If number of changes seen is less than min threshold, then fail
+#	6. If number of changes seen is more than max threshold, then fail
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/tests/functional/mmp/mmp.cfg
+. $STF_SUITE/tests/functional/mmp/mmp.kshlib
+
+verify_runnable "both"
+
+UBER_CHANGES=0
+
+function cleanup
+{
+	default_cleanup_noexit
+	set_tunable64 zfs_txg_timeout $TXG_TIMEOUT_DEFAULT
+	log_must rm -f $PREV_UBER $CURR_UBER
+	log_must mmp_clear_hostid
+}
+
+log_assert "Ensure MMP uberblocks update at the correct interval"
+log_onexit cleanup
+
+log_must set_tunable64 zfs_txg_timeout $TXG_TIMEOUT_LONG
+log_must mmp_set_hostid $HOSTID1
+
+default_setup_noexit $DISK
+log_must zpool set multihost=on $TESTPOOL
+
+log_must zdb -u $TESTPOOL > $PREV_UBER
+
+SECONDS=0
+while [[ $SECONDS -le 10 ]]; do
+	log_must zdb -u $TESTPOOL > $CURR_UBER
+	if ! diff -u "$CURR_UBER" "$PREV_UBER"; then
+		(( UBER_CHANGES = UBER_CHANGES + 1 ))
+		log_must mv "$CURR_UBER" "$PREV_UBER"
+	fi
+done
+
+log_note "Uberblock changed $UBER_CHANGES times"
+
+if [[ $UBER_CHANGES -lt 8 ]]; then
+	log_fail "Fewer uberblock writes occured than expected (10)"
+fi
+
+if [[ $UBER_CHANGES -gt 12 ]]; then
+	log_fail "More uberblock writes occured than expected (10)"
+fi
+
+log_pass "Ensure MMP uberblocks update at the correct interval passed"
diff --git a/tests/zfs-tests/tests/functional/mmp/setup.ksh b/tests/zfs-tests/tests/functional/mmp/setup.ksh
new file mode 100755
index 000000000000..fde5e3bb7773
--- /dev/null
+++ b/tests/zfs-tests/tests/functional/mmp/setup.ksh
@@ -0,0 +1,32 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+# CDDL HEADER END
+#
+
+#
+# Copyright (c) 2017 by Lawrence Livermore National Security, LLC.
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/tests/functional/mmp/mmp.cfg
+
+verify_runnable "global"
+
+if [ -e $HOSTID_FILE ]; then
+	log_unsupported "System has existing $HOSTID_FILE file"
+fi
+
+log_must set_tunable64 zfs_multihost_history $MMP_HISTORY
+
+log_pass "mmp setup pass"