A disk array system includes a memory that stores first key data inherent to the disk array system, and a disk controller that controls data input/output to/from disk drives. Each of the disk drives includes a disk medium, and an HDD controller, the disk medium having a system area that stores second key data inherent to a disk array system, and a data area that stores user data, the HDD controller controlling data input/output to/from the system area and the data area. The HDD controller, upon a disk drive from among the disk drives being mounted in the disk array system, comparing the first key data and the second key data, and if they do not correspond to each other, operating in an operation mode in which read access from the disk controller to the data area is prohibited.