ZFSD(8)                 FreeBSD System Manager's Manual                ZFSD(8)

NAME
     zfsd - ZFS fault management daemon

SYNOPSIS
     zfsd [-d]

DESCRIPTION
     zfsd attempts to resolve ZFS faults that the kernel can't resolve by
     itself.  It listens to devctl(4) events, which are how the kernel
     notifies userland of events such as I/O errors and disk removals.  zfsd
     attempts to resolve these faults by activating or deactivating hot spares
     and onlining offline vdevs.

     The following options are available:

     -d      Run in the foreground instead of daemonizing.

     System administrators never interact with zfsd directly.  Instead, they
     control its behavior indirectly through zpool configuration.  There are
     two ways to influence zfsd: assigning hotspares and setting pool
     properties.  Currently, only the autoreplace property has any effect.
     See zpool(8) for details.

     zfsd will attempt to resolve the following types of fault:

     device removal
        When a leaf vdev disappears, zfsd will activate any available
        hotspare.

     device arrival
        When a new GEOM device appears, zfsd will attempt to read its ZFS
        label, if any.  If it matches a previously removed vdev on an active
        pool, zfsd will online it.  Once resilvering completes, any active
        hotspare will detach automatically.

        If the new device has no ZFS label but its physical path matches the
        physical path of a previously removed vdev on an active pool, and that
        pool has the autoreplace property set, then zfsd will replace the
        missing vdev with the newly arrived device.  Once resilvering
        completes, any active hotspare will detach automatically.

     vdev degrade or fault events
        If a vdev becomes degraded or faulted, zfsd will activate any
        available hotspare.

     I/O errors
        If a leaf vdev generates more than 50 I/O errors in a 60 second
        period, then zfsd will mark that vdev as FAULTED.  ZFS will no longer
        issue any I/Os to it.  zfsd will activate a hotspare if one is
        available.

     Checksum errors
        If a leaf vdev generates more than 50 checksum errors in a 60 second
        period, then zfsd will mark that vdev as DEGRADED.  ZFS will still use
        it, but zfsd will activate a spare anyway.

     Spare addition
        If the system administrator adds a hotspare to a pool that is already
        degraded, zfsd will activate the spare.

     Resilver complete
        zfsd will detach any hotspare once a permanent replacement finishes
        resilvering.

     Physical path change
        If the physical path of an existing disk changes, zfsd will attempt to
        replace any missing disk with the same physical path, if its pool's
        autoreplace property is set.

     zfsd will log interesting events and its actions to syslog with facility
     daemon and identity [zfsd].

FILES
     /var/db/zfsd/cases
        When zfsd exits, it serializes any unresolved casefiles here, then
        reads them back in when next it starts up.

SEE ALSO
     devctl(4), zpool(8)

HISTORY
     zfsd first appeared in FreeBSD 11.0.

AUTHORS
     zfsd was originally written by Justin Gibbs <gibbs@FreeBSD.org> and
     Alan Somers <asomers@FreeBSD.org>

TODO
     In the future, zfsd should be able to resume a pool that became suspended
     due to device removals, if enough missing devices have returned.

FreeBSD 13.1-RELEASE-p6         April 18, 2020         FreeBSD 13.1-RELEASE-p6