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.Dd February 20, 2024 .Dt ZFSD 8 .Os .Sh NAME .Nm zfsd .Nd ZFS fault management daemon .Sh SYNOPSIS .Nm .Op Fl d .Sh DESCRIPTION .Nm attempts to resolve ZFS faults that the kernel can't resolve by itself. It listens to .Xr devctl 4 events, which are how the kernel notifies userland of events such as I/O errors and disk removals. .Nm attempts to resolve these faults by activating or deactivating hot spares and onlining offline vdevs.
p The following options are available: l -tag -width indent t Fl d Run in the foreground instead of daemonizing. .El
p System administrators never interact with .Nm directly. Instead, they control its behavior indirectly through zpool configuration. There are two ways to influence .Nm : assigning hot spares and setting pool properties. Currently, only the .Em autoreplace property has any effect. See .Xr zpool 8 for details.
p .Nm will attempt to resolve the following types of fault: l -tag -width a t device removal When a leaf vdev disappears, .Nm will activate any available hot spare. t device arrival When a new GEOM device appears, .Nm will attempt to read its ZFS label, if any. If it matches a previously removed vdev on an active pool, .Nm will online it. Once resilvering completes, any active hot spare will detach automatically.
p 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 .Nm will replace the missing vdev with the newly arrived device. Once resilvering completes, any active hot spare will detach automatically. t vdev degrade or fault events If a vdev becomes degraded or faulted, .Nm will activate any available hot spare. t I/O errors By default, if a leaf vdev generates more than 50 I/O errors in a 60 second period, then .Nm will mark that vdev as .Em FAULTED . ZFS will no longer issue any I/Os to it. .Nm will activate a hot spare if one is available. The defaults can be changed by setting the .Em io_n and/or .Em io_t vdev properties. See .Xr vdevprops 7 for details. t I/O delays By default, if a leaf vdev generates more than delayed 8 I/O events in a 60 second period, then .Nm will mark that vdev as .Em FAULTED . ZFS will no longer issue any I/Os to it. .Nm will activate a hot spare if one is available. The defaults can be changed by setting the .Em slow_io_n and/or .Em slow_io_t vdev properties. See .Xr vdevprops 7 for details. t Checksum errors By default, if a leaf vdev generates more than 50 checksum errors in a 60 second period, then .Nm will mark that vdev as .Em DEGRADED . ZFS will still use it, but zfsd will also activate a hot spare if one is available. The defaults can be changed by setting the .Em checksum_n and/or .Em checksum_t vdev properties. See .Xr vdevprops 7 for details. t Spare addition If the system administrator adds a hot spare to a pool that is already degraded, .Nm will activate the spare. t Resilver complete .Nm will detach any hot spare once a permanent replacement finishes resilvering. t Physical path change If the physical path of an existing disk changes, .Nm will attempt to replace any missing disk with the same physical path, if its pool's autoreplace property is set. .El
p .Nm will log interesting events and its actions to syslog with facility .Em daemon and identity .Op zfsd . .El .Sh FILES l -tag -width a -compact t Pa /var/db/zfsd/cases When .Nm exits, it serializes any unresolved casefiles here, then reads them back in when next it starts up. .El .Sh SEE ALSO .Xr devctl 4 , .Xr vdevprops 7 , .Xr zpool 8 .Sh HISTORY .Nm first appeared in .Fx 11.0 . .Sh AUTHORS .Nm was originally written by .An Justin Gibbs Aq Mt gibbs@FreeBSD.org and .An Alan Somers Aq Mt asomers@FreeBSD.org .Sh TODO In the future, .Nm should be able to resume a pool that became suspended due to device removals, if enough missing devices have returned.