Abstract: If a disk array device according to the invention initially has four disk devices, which is the smallest number of disk devices for RAID5 (3D+P), the storage region of each of the four disk devices is equally divided by four to produce partitions. Then, four partitions are selected respectively from the four disk devices and combined to form a redundancy group so that a total of four redundancy groups are formed. When another disk device is added, its storage region is also equally divided by four. Four partitions are selected from the four redundancy groups, one from each of the disk devices, and the data of the selected four partitions are copied to the four partitions of the added disk device. After the completion of the copying, the origin of copying partitions are excluded from the original redundancy groups and the corresponding four destination of copying partitions are incorporated to replace the excluded partitions.

Abstract: If a disk array device according to the invention initially has four disk devices, which is the smallest number of disk devices for RAID5 (3D+P), the storage region of each of the four disk devices is equally divided by four to produce partitions. Then, four partitions are selected respectively from the four disk devices and combined to form a redundancy group so that a total of four redundancy groups are formed. When another disk device is added, its storage region is also equally divided by four. Four partitions are selected from the four redundancy groups, one from each of the disk devices, and the data of the selected four partitions are copied to the four partitions of the added disk device. After the completion of the copying, the origin of copying partitions are excluded from the original redundancy groups and the corresponding four destination of copying partitions are incorporated to replace the excluded partitions.

Abstract: A disc array apparatus, having a presupposed response time, that includes several disc units for storing data transmitted from a host apparatus and an array controller for controlling a data transfer between disc units and the host apparatus. The array controller has a performance detector for detecting response times of the disc units, a correction value generator for calculating a correction value based on a difference between the response time detected for each of the disc units and a reference value, and a response timing corrector for correcting a time value at which an access end report is sent to the host apparatus at the presupposed response time, using the correction value.