A disk array system having first and second housings and a controller for controlling the first and second housings. Fiber channel hard disk drives are received in the first housing, and serial ATA hard disk drives are received in the second housing. When reading data stored in a serial ATA hard disk drive in the second housing, the controller reads a plurality of pieces of data including the data to be read and parity data for the plurality of pieces of data from all the hard disk drives of an RAID group to which the hard disk drive storing the data to be read belongs. Thus, the controller examines whether the plurality of pieces of data including the data to be read are written in the hard disk drives with erroneous contents or not.