A disk array system, upon detecting a failure in any data disk from among a plurality of data disks providing one or more RAID groups, conducting a correction copy to any spare disk, using one or more other data disks belonging to the same RAID group as the data disk causing the failure. When the data disk causing the failure has been replaced with a new data disk, the disk array system alters the management so that the data disk can be managed as a spare disk, and the spare disk can be managed as a data disk.