---
name: "zfsd"
section: "8"
platform: "freebsd"
package: "base"
version: "16.0-CURRENT-20261027-61c70dc16a79"
release: "FreeBSD 16.0-CURRENT (2026-10-27)"
platforms: ["freebsd"]
url: "https://new.carta.tech/zfsd"
---

# zfsd(8)

ZFS fault management daemon

## 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)](/devctl/4.md) 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 hot spares and setting pool properties. Currently, only the *autoreplace* property has any effect. See [zpool(8)](/zpool/8.md) for details.

**zfsd** will attempt to resolve the following types of fault:

- device removal

  When a leaf vdev disappears, **zfsd** will activate any available hot spare.

- 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 hot spare 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 hot spare will detach automatically.

- vdev degrade or fault events

  If a vdev becomes degraded or faulted, **zfsd** will activate any available hot spare.

- I/O errors

  By default, 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 hot spare if one is available. The defaults can be changed by setting the *io\_n* and/or *io\_t* vdev properties. See [vdevprops(7)](/vdevprops/7.md) for details.

- I/O delays

  By default, if a leaf vdev generates more than delayed 8 I/O events 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 hot spare if one is available. The defaults can be changed by setting the *slow\_io\_n* and/or *slow\_io\_t* vdev properties. See [vdevprops(7)](/vdevprops/7.md) for details.

- Checksum errors

  By default, 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 also activate a hot spare if one is available. The defaults can be changed by setting the *checksum\_n* and/or *checksum\_t* vdev properties. See [vdevprops(7)](/vdevprops/7.md) for details.

- Spare addition

  If the system administrator adds a hot spare to a pool that is already degraded, **zfsd** will activate the spare.

- Resilver complete

  **zfsd** will detach any hot spare 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)](/devctl/4.md), [vdevprops(7)](/vdevprops/7.md), [zpool(8)](/zpool/8.md)

## 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.