Missing Devices in a ZFS Storage Pool

If a device is completely removed from the system, ZFS detects that the device cannot be opened and places it in the UNAVAIL state. Depending on the data replication level of the pool, this might or might not result in the entire pool becoming unavailable. If one disk in a mirrored or RAID-Z device is removed, the pool continues to be accessible. If all components of a mirror are removed, if more than one device in a RAID-Z (raidz1) device is removed, or if a single-disk, top-level device is removed, the pool becomes FAULTED. No data is accessible until the device is reattached.