Skip to content

Latest commit

 

History

History
executable file
·
141 lines (111 loc) · 4.48 KB

disk-types.md

File metadata and controls

executable file
·
141 lines (111 loc) · 4.48 KB
Raw

DSM Disk Types

This document is incomplete

Synology added many more or less hacky things to the kernel. Some of their best additions are in the SCSI subsystem. Two of them, working together, are detection of disk ports and types.

Normally Linux kernel doesn't care where drive physically is, and it doesn't track what type of a port it is connected to. All the SCSI subsystem cares about is that the drive "speaks" SCSI. This is a very flexible approach as nothing has to distinguish whether it's talking to a USB flash driver or a SATA HDD. However, in a NAS scenario we need to know if something is an internal SATA drive or an external USB stick.

Port types

Syno kernel adds one of the following types to any SCSI host port:

// include/scsi/scsi_host.h
enum {
  SYNO_PORT_TYPE_SATA = 1,
  SYNO_PORT_TYPE_USB = 2,
  SYNO_PORT_TYPE_SAS = 3,
};

That value is saved in (scsi_device *)sdp->host->hostt->syno_port_type and is fixed during SCSI driver initialization.

Disk types

The customized kernel contain another layer above port types dealing with disk types. The disk type represents a logical role of a given block device in the system. It can be any of the following:

# drivers/scsi/sd.h

typedef enum __syno_disk_type {
    SYNO_DISK_UNKNOWN = 0,
    SYNO_DISK_SATA,
    SYNO_DISK_USB,
    SYNO_DISK_SYNOBOOT,
    SYNO_DISK_ISCSI,
    SYNO_DISK_SAS,
#ifdef MY_ABC_HERE
    SYNO_DISK_CACHE,  
#endif  
    SYNO_DISK_END,  
}SYNO_DISK_TYPE;

These types are determined in the drivers/scsi/sd.c:sd_probe(), called as the first function after drive appears in the system. All but one type should be self-explanatory. The SYNO_DISK_SYNOBOOT is discussed in more details in the "Synoboot" section.

SMART support

Since v7 the following types are expected to support SMART, or they will be constantly marked as unhealthy. This will case these disks to be unusable for pools creation (rendering them useless):

  • SYNO_DISK_SATA
  • SYNO_DISK_SAS
  • SYNO_DISK_CACHE

Special cases

VirtIO SCSI disks

Disks connected using VirtIO driver can be passed via SCSI or SATA. Using the former allows for many more drives, while the latter has more widespread support. The sd.c SCSI driver contains a special provisioning for SCSI VirtIO disks, treating them exactly like SYNO_DISK_SATA type. However, that provisioning is active for limited subset of platforms. Based on the constants in the GPL code it's probably only active in VDSM mode:

//sd.c:sd_probe()

#if defined(MY_ABC_HERE) || defined(CONFIG_SYNO_NEXTKVMX64)
  if (strcmp(sdp->host->hostt->name, "Virtio SCSI HBA") == 0){
#ifdef MY_ABC_HERE
    while (virtdev) {
      if (virtdev->driver && virtdev->driver->name && !strcmp(virtdev->driver->name, "virtio-pci")) {
        pcidev = to_pci_dev(virtdev);
        break;
      }
      virtdev = virtdev->parent;
    }
    if (pcidev && PCI_SLOT(pcidev->devfn) == CONFIG_SYNO_KVMX64_PCI_SLOT_BOOT) {
      return SYNO_DISK_SYNOBOOT;
    }
#endif  
    return SYNO_DISK_SATA;
  }
#endif

Flags

There are some flags associated with disks. This is by no means a complete list (see drivers/scsi/sd.c).

System disk flag

This flag, present in struct gendisk->systemdisk (include/linux/genhd.h) denotes if the disk may potentially contain a system partition. Its absence blocks mdadm from automatically assembling the array during boot:

md: Autodetecting RAID arrays.
md: deny sdc1.
md: export_rdev(sdc1)
md: deny sdc2.
md: export_rdev(sdc2)
md: Scanned 2 and added 0 devices.
md: autorun ...
md: ... autorun DONE.

This in turn causes the system to boot into initramfs state after installation, as there are no OS disks to mount. The method responsible for checking this is blDenyDisks() (drivers/md/md.c) called from the autostart_arrays():

if (blDenyDisks(rdev->bdev)) {
    char b[BDEVNAME_SIZE];

    printk(KERN_INFO "md: deny %s.\n",
           bdevname(rdev->bdev,b));

    export_rdev(rdev);
    continue;
}

The flag is set in sd_probe() (drivers/scsi/sd.c) for types SYNO_DISK_SAS and SYNO_DISK_SATA. There's nothing custom for the SAS disks. However, the SATA one must be connected to a port considered :

    case SYNO_DISK_SATA:
#ifdef MY_ABC_HERE
        ap = ata_shost_to_port(sdp->host);
         
        if (NULL != ap && !syno_is_synology_pm(ap)) {
#endif  
            gd->systemDisk = 1;
#ifdef MY_ABC_HERE
        }

todo: add more flags