With respect to each head mounted on a hard disk, an area accessed by the head is obtained in advance and managed as disk information. Then, if a read error or a write error has occurred during operation, the corresponding head is identified on the basis of a logical block address at which the error has occurred. If a read error or a write error caused by the identified head has occurred multiple times, only data stored in an area accessed by the head is transferred to another hard disk. After the completion of the data transfer, the hard disk with the failed head and the other hard disk serving as the destination of the data transfer are used as hard disks constituting the same RAID array.
