I've got a system with 4 disks set up as raid10. All disks are usable, and mdadm all states them with UUUU.
Due to a recent system crash, the raid is currently
reconstruction the raid as it was marked as "not clean," and a
reconstruction process was started.
On a closer look smartctl shows problems on one disk:
sd 0:0:0:0: [sda] Unhandled
…