Determining if a Device Can Be Replaced

For a device to be replaced, the pool must be in the ONLINE state. The device must be part of a redundant configuration, or it must be healthy (in the ONLINE state). If the disk is part of a redundant configuration, sufficient replicas from which to retrieve good data must exist. If two disks in a four-way mirror are faulted, then either disk can be replaced because healthy replicas are available. However, if two disks in a four-way RAID-Z (raidz1) device are faulted, then neither disk can be replaced because not enough replicas from which to retrieve data exist. If the device is damaged but otherwise online, it can be replaced as long as the pool is not in the FAULTED state. However, any bad data on the device is copied to the new device unless there are sufficient replicas with good data.

In the following configuration, the disk c1t1d0 can be replaced, and any data in the pool is copied from the good replica, c1t0d0.

    mirror            DEGRADED
    c1t0d0             ONLINE
    c1t1d0             FAULTED

The disk c1t0d0 can also be replaced, though no self-healing of data can take place because no good replica is available.

In the following configuration, neither of the faulted disks can be replaced. The ONLINE disks cannot be replaced either, because the pool itself is faulted.

    raidz              FAULTED
    c1t0d0             ONLINE
    c2t0d0             FAULTED
    c3t0d0             FAULTED
    c4t0d0             ONLINE

In the following configuration, either top-level disk can be replaced, though any bad data present on the disk is copied to the new disk.

c1t0d0         ONLINE
c1t1d0         ONLINE

If either disk were faulted, then no replacement could be performed because the pool itself would be faulted.