Rebuild fails to complete

This case is mostly about maintenance, when 220 Black Armor fails to complete resync

I have a Seagate black armor 220 which keeps trying to repair a volume after a had drive failed as part of RAID1. I replaced the disk, added the member drive ran the S.M.A.R.T checks on the drives and started to recover … it gets to around 80% and the restarts. There are no error messages and this has been looping for about a week now…

Any ideas as to why it wont complete the recovery process and rebuild the raid volume? or how I can trouble shoot it?

This one is easy. The NAS is still readable, so the troubleshooting consists of five steps,

  1. Back up data from NAS to some other location.
  2. Destroy RAID1 in NAS.
  3. Replace disk which is still not replaced.
  4. Reconfigure RAID1 and wait for resync.
  5. Restore from backup.

The problem most likely is that the second (non-replaced) disk has developed a problem; SMART test can sometimes miss a bad sector, or the interpretation of SMART data either by the customer or by the NAS firmware is excessively tolerant. The inability to complete the rebuild is more significant observation than a SMART test result.