According to adaptec support site, data on a disk got corrupted. The disk is physically fine and thats why it shows up as optimal. The solution is to reinitialize the disk. The only problem is I can't figure out which disk has the problem. Adaptec Storage Manager just says raid is degraded and all disks are optimal with no more information. Any ideas?
The disk that caused this should no longer be part of the active array. Maybe it was re-assigned as the hotspare or you need to scan for un-assigned hard disks?