Repairing a Missing ZFS Device

If a device cannot be opened, it displays as UNAVAILABLE in the zpool status output. This status means that ZFS was unable to open the device when the pool was first accessed, or the device has since become unavailable. If the device causes a top-level virtual device to be unavailable, then nothing in the pool can be accessed. Otherwise, the fault tolerance of the pool might be compromised. In either case, the device simply needs to be reattached to the system to restore normal operation.

For example, you might see a message similar to the following from fmd after a device failure:

# zpool status -x
  pool: tank
 state: DEGRADED
status: One or more devices could not be opened.  Sufficient replicas exist for
        the pool to continue functioning in a degraded state.
action: Attach the missing device and online it using 'zpool online'.
 scrub: resilver completed with 0 errors on Fri Mar 10 11:08:29 2006

        NAME         STATE     READ WRITE CKSUM
        tank         DEGRADED     0     0     0
          mirror     DEGRADED     0     0     0
            c0t3d0   UNAVAIL      0     0     0  cannot open
            c1t1d0   ONLINE       0     0     0

You can see from this output that the missing device c0t3d0 is not functioning. If you determine that the drive is faulty, replace the device.

Then, use the zpool online command to online the replaced device. For example:

# zpool online tank c0t3d0

Confirm that the pool with the replaced device is healthy.

# zpool status -x tank
pool 'tank' is healthy

Physically Reattaching the Device

Exactly how a missing device is reattached depends on the device in question. If the device is a network-attached drive, connectivity should be restored. If the device is a USB or other removable media, it should be reattached to the system. If the device is a local disk, a controller might have failed such that the device is no longer visible to the system. In this case, the controller should be replaced at which point the disks will again be available. Other pathologies can exist and depend on the type of hardware and its configuration. If a drive fails and it is no longer visible to the system (an unlikely event), the device should be treated as a damaged device. Follow the procedures outlined in Repairing a Damaged Device.

Notifying ZFS of Device Availability

Once a device is reattached to the system, ZFS might or might not automatically detect its availability. If the pool was previously faulted, or the system was rebooted as part of the attach procedure, then ZFS automatically rescans all devices when it tries to open the pool. If the pool was degraded and the device was replaced while the system was up, you must notify ZFS that the device is now available and ready to be reopened by using the zpool online command. For example:

# zpool online tank c0t3d0