Disk controller

A disk controller includes a determining unit for determining whether check codes added to data read from a disk drive are first type check codes or second type check codes, and a check code conversion unit. The check code conversion unit includes conversion unit for converting, if the check codes added to the read data are first type check codes, the first type check codes into second type check codes and a writing unit for writing the data provided with the second type check codes into the disk drive. The disk controller also includes a control unit for performing background processing, which is performed at a time different from processing performed when a data read request or a data write request is sent from a host device, by reading data provided with check codes from the disk drive and by starting check code conversion processing performed by the check code conversion unit.