The present invention efficiently recovers an error drive by suppressing futile copying. When the number of errors of the disk drive is equal to or more than a first threshold, data stored in the disk drive is copied to a spare drive by a drive copy section. When the number of errors of the disk drive is equal to or more than a second threshold prior to completion of the drive copy, the disk drive is closed, and a correction copy by a correction copy section is started in place of the drive copy. The correction copy section starts the correction copy from the position where the drive copy is interrupted by taking over the drive copy completion position (copy interrupt position) managed by a copy progress condition management section.