FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/man/man8/zpool-scrub.8

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    .Dd July 25, 2021
    .Dt ZPOOL-SCRUB 8
    .Os
    .
    .Sh NAME
    .Nm zpool-scrub
    .Nd begin or resume scrub of ZFS storage pools
    .Sh SYNOPSIS
    .Nm zpool
    .Cm scrub
    .Op Fl s Ns | Ns Fl p
    .Op Fl w
    .Ar pool Ns …
    .
    .Sh DESCRIPTION
    Begins a scrub or resumes a paused scrub.
    The scrub examines all data in the specified pools to verify that it checksums
    correctly.
    For replicated
    .Pq mirror, raidz, or draid
    devices, ZFS automatically repairs any damage discovered during the scrub.
    The
    .Nm zpool Cm status
    command reports the progress of the scrub and summarizes the results of the
    scrub upon completion.
    .Pp
    Scrubbing and resilvering are very similar operations.
    The difference is that resilvering only examines data that ZFS knows to be out
    of date
    .Po
    for example, when attaching a new device to a mirror or replacing an existing
    device
    .Pc ,
    whereas scrubbing examines all data to discover silent errors due to hardware
    faults or disk failure.
    .Pp
    Because scrubbing and resilvering are I/O-intensive operations, ZFS only allows
    one at a time.
    .Pp
    A scrub is split into two parts: metadata scanning and block scrubbing.
    The metadata scanning sorts blocks into large sequential ranges which can then
    be read much more efficiently from disk when issuing the scrub I/O.
    .Pp
    If a scrub is paused, the
    .Nm zpool Cm scrub
    resumes it.
    If a resilver is in progress, ZFS does not allow a scrub to be started until the
    resilver completes.
    .Pp
    Note that, due to changes in pool data on a live system, it is possible for
    scrubs to progress slightly beyond 100% completion.
    During this period, no completion time estimate will be provided.
    .
    .Sh OPTIONS
    .Bl -tag -width "-s"
    .It Fl s
    Stop scrubbing.
    .It Fl p
    Pause scrubbing.
    Scrub pause state and progress are periodically synced to disk.
    If the system is restarted or pool is exported during a paused scrub,
    even after import, scrub will remain paused until it is resumed.
    Once resumed the scrub will pick up from the place where it was last
    checkpointed to disk.
    To resume a paused scrub issue
    .Nm zpool Cm scrub
    again.
    .It Fl w
    Wait until scrub has completed before returning.
    .El
    .Sh EXAMPLES
   .Ss Example 1
   Status of pool with ongoing scrub:
   .sp
   .Bd -literal -compact
   .No # Nm zpool Cm status
     ...
     scan: scrub in progress since Sun Jul 25 16:07:49 2021
           403M scanned at 100M/s, 68.4M issued at 10.0M/s, 405M total
           0B repaired, 16.91% done, 00:00:04 to go
     ...
   .Ed
   .Pp
   Where metadata which references 403M of file data has been
   scanned at 100M/s, and 68.4M of that file data has been
   scrubbed sequentially at 10.0M/s.
   .Sh PERIODIC SCRUB
   On machines using systemd, scrub timers can be enabled on per-pool basis.
   .Nm weekly
   and
   .Nm monthly
   timer units are provided.
   .Bl -tag -width Ds
   .It Xo
   .Xc
   .Nm systemctl
   .Cm enable
   .Cm zfs-scrub-\fIweekly\fB@\fIrpool\fB.timer
   .Cm --now
   .It Xo
   .Xc
   .Nm systemctl
   .Cm enable
   .Cm zfs-scrub-\fImonthly\fB@\fIotherpool\fB.timer
   .Cm --now
   .El
   .
   .Sh SEE ALSO
   .Xr systemd.timer 5 ,
   .Xr zpool-iostat 8 ,
   .Xr zpool-resilver 8 ,
   .Xr zpool-status 8

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