A RAID control apparatus and control method. The RAID control apparatus includes disk devices and disk control devices including a cache memory that stores cache data of a logical unit, and control unit, upon the logical units present in different disk devices being concatenated to each other, switching in-charge disk control devices such that a disk control device is in charge of access to the concatenated logical units without writing back the cache data stored in a cache memory of a source disk control device to the disk device.