Provided are a storage controller and a storage control method capable of improving the transaction performance. This storage controller includes a disk controller for receiving a read command and a write command from a host computer, and an external disk controller and an internal disk device for sending and receiving data to and from the disk controller. A storage device of the external disk controller or the internal disk controller processes the access from the disk controller in physical sub-block units. When the disk controller is to access the storage device of the external disk controller or the internal disk device in logical sub-block units in which an additional code containing a guarantee code is added to user data, it makes such access in minimum common multiple units of logical sub-blocks and physical sub-blocks, and changes the guarantee code length.