Last week my SMART diagnostics utility, CrystalDiskInfo, reported that the external hard drive that I was saving my backups to had suddenly reported 900+ reallocated sectors. I double-checked to confirm, then ordered a replacement drive.

I spent all of this week copying data from that drive to the new drive. But toward the end of the copy, something peculiar happened. CrystalDiskInfo popped up an alert that the reallocated sector count had gone back down to 0.

I know that when SMART detects a read error on a block, it adds that block to the current pending reallocation list. If it subsequently is successfully written or read later, it is removed from the list and assumed to be fine, but if a subsequent write fails, it is marked bad and added to the reallocated sector count.

What concerns me most is that I've never read anywhere that a sector can be recovered as "good" after it has been marked as a bad sector and remapped.

I've just finished running an extended SMART diagnostic, and it found no surface errors. Now I'm doubtful that the manufacturer will honor a warranty claim if the SMART info does not report any problems.

Has anyone had this happen? If so, then is the drive, indeed, okay, or should I be concerned about an imminent failure?