A RAID system includes a RAID controller that sends to a disc apparatus data to be encrypted by a data relay apparatus connected to the RAID controller and the disk apparatus. When receiving a data transfer request packet indicating a first receivable size, the data relay apparatus establishes a second receivable size that is equal to or greater than the first receivable size and that is a multiple of an encryption data size. When the RAID controller receives a data transfer request packet containing the established second receivable size, and in response to the data transfer request packet thus received, the data relay apparatus receives data of the second receivable size sent from the RAID controller. The data relay apparatus also encrypts the received data in units of the encryption data size, and then the encrypted data is sent to the disk apparatus in units of the first receivable size.