Patent ID: 7028216

Claim:
A disk array system comprising: a channel adapter for controlling data transfer with respect to a host device; a plurality of data disk drives configuring a RAID group, at least one spare disk drive provided as a spare for the data disk drives; a disk adapter for controlling data transfer with respect to the data disk drives and the spare disk drive; a cache memory used by the channel adapter and the disk adapter for storing data; a control memory used by the channel adapter and the disk adapter for storing control information; a backup storage provided separately from the data disk drives and the spare disk drive; a first control unit provided in the disk adapter for observing occurrence of access error with respect to the data disk drives, the first control unit, when the frequency of occurrence of the access error exceeds a predetermined threshold, copying data stored in the data disk drive exceeding the threshold to the spare disk drive via the cache memory; a second control unit provided in the disk adapter for processing access request directed to the RAID group during the copying process, the second control unit making the backup storage take over a write request directed to the RAID group; and a third control unit provided in the disk adapter for copying data written in the backup storage by the second control unit to the data disk drives and the spare disk drive other than the data disk drive exceeding the threshold when the copying process by the fist control unit is finished.