Patent ID: 7562249

Claim:
A RAID system for accessing a connected disk device and executing an I/O request according to the I/O request requested by a host, comprising: a plurality of said disk devices constituting a RAID; and a controller for executing an operation of reading data of a disk device, other than a failed disk device, when one of said plurality of disk devices failed, and writing the data to a spare disk device or a new disk device in parts for a plurality of times to execute Rebuild, or Copy back processing for reconstructing the RAID configuration, wherein said controller judges whether a normal I/O request, including an I/O request from said host, does not arrive for a predetermined time, concurrently executes read processing of one disk device and write processing of another disk device in said Rebuild or Copy back if said normal I/O request does not arrive for a predetermined time, and executes alternately said normal I/O request and a request of one of read and write of said disk device for one time of said Rebuild or Copy back if said normal I/O request arrives in a predetermined time.