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Resilver performance tuning #14428

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wants to merge 2 commits into from
Closed

Resilver performance tuning #14428

wants to merge 2 commits into from

Commits on Jan 26, 2023

  1. Increase default zfs_scan_vdev_limit to 16MB 

    For HDD based pools the default zfs_scan_vdev_limit of 4M
per-vdev can significantly limit the maximum scrub performance.
Increasing the default to 16M can double the scrub speed from
80 MB/s per disk to 160 MB/s per disk.

This does increase the memory footprint during scrub/resilver
but given the performance win this is a reasonable trade off.
Memory usage is capped at 1/4 of arc_c_max.  Note that number
of outstanding I/Os has not changed and is still limited by
zfs_vdev_scrub_max_active.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
    @behlendorf
    behlendorf committed Jan 26, 2023
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  2. Increase default zfs_rebuild_vdev_limit to 64MB 

    When testing distributed rebuild performance with more capable
hardware it was observed than increasing the zfs_rebuild_vdev_limit
to 64M reduced the rebuild time by 17%.  Beyond 64MB there was
some improvement (~2%) but it was not significant when weighed
against the increased memory usage. Memory usage is capped at 1/4
of arc_c_max.

Additionally, vr_bytes_inflight_max has been moved so it's updated
per-metaslab to allow the size to be adjust while a rebuild is
running.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
    @behlendorf
    behlendorf committed Jan 26, 2023
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