Patent ID: 7539816

Claim:
A disk control device connecting a first disk drive and a second disk drive, comprising: a first queue storing write requests from a cache memory and read requests from a host for the first disk drive in chronological order; a second queue storing write requests from the cache memory for the second disk drive; and a controller controlling the disk control device including disk access means for sequentially reading requests stored in the first queue for the first disk drive to access the first disk drive, queue changing means for changing a storage location of write requests to the second queue when the number of write requests stored in the first queue is greater than a predetermined value, request-allocation means for directly storing the write requests into the second queue and for storing only the read requests into the first queue after queue changing, write means for writing the write requests stored in the second queue into the second disk drive, and writing back means for writing back the write requests stored in the second disk drive to the first disk drive when the number of write requests stored in the first queue becomes smaller than a predetermined threshold.