Disk Disconnected after power loss

[itteam]

System detected loss of power in the UPS and went into autoprotect mode.
Upon resuming, we have NOT QUITE the same as the "disk failed/disk unplugged" error in the hot post:

21:13:58 Failed to access the installed drive; check the drive for errors.
21:14:22 RAID group 1 is degraded
21:14:26 Host Disk 4 Disconnected
21:14:26 Skipped rebuilding RAID group 1

RAID 6 using 4 disks with a spare sitting in slot 5 (8 bay unit in my sig).
How best to proceed?

[dolbyman]

swap the faulty disk (spare should kick in) and see if you can set it as new spare

if so (disk was broken)
if not (slot could be broken)

[itteam]

Thank you. To be clear, we haven't tried anything yet.
Are you assuming I already tried either rebooting AND/OR pulling and reinserting disk 4 ?
Or it's not suggested to bother attempting to maintain existing disk/content in the RAID (except as new spare) - just move on to the new disk ?

[dolbyman]

No I didn't think you did anything yet , that why I asked to swap the drive

[itteam]

QNAP support asked to first remove and reseat disk 4 in the same slot - which we did. It reported as detected and the RAID started and has since completed rebuild AOK.
We will be keeping a close watch on this one, and I will update.

[itteam]

Follow up Almost 2 months on, and we've had no further issues with this unit.