RAID 2 is the only RAID level that can "repair" errors, the other RAID levels can only detect them. When they find that the information needed does not make sense, they will simply rebuild it. This is done with calculations, using information on the other disks. If that information is missing or wrong, they cannot do much. Because it uses Hamming codes, RAID 2 can find out which piece of the information is wrong, and correct only that piece.