Patent ID: 7080196

Claim:
A RAID apparatus comprising: a plurality of physical disk units storing a plurality of copies of each of logical volumes; and a disk controller accessing any of the physical disk units which stores a designated logical volume to thereby access said designated logical volume, said disk controller including: a memory storing a logical volume structure table storing a status and indicating physical disk units of each logical volume, and a disk management table storing statuses and the number of operations of each physical disk unit; and a control unit which refers to said status in said logical volume structure table with a designated logical volume, judges whether or not said status information of said logical volume indicates abnormal, selects said single physical disk unit on which said designated logical volume is allocated by comparison of the operation numbers in said disk management table when a plurality of physical disk units storing copies of said designated logical volume are normal, and selects a normal physical disk unit among said plurality of physical disk units of said designated logical volume indicated by said logical volume structure table by referring to said statuses of each physical disk unit in said disk management table when said status information of said logical volume indicates abnormal.