Proposed are a disk array apparatus and a control method thereof which facilitate data processing such as write processing and read processing even if the block sizes handled by a host computer are different.If a first write command is received from the host computer, the controller of the disk array apparatus divides first write data into a plurality of second write data, and adds a first guarantee code and writes this data to the plurality of first storage devices; if a first read command is received from the host computer, the controller reads a plurality of first read data from the plurality of first storage devices, generates second read data which is obtained by combining [the plurality of first read data], and adds a second guarantee code [to the second read data] and transmits this data to the host computer; if a second write command is received from the host computer, the controller generates fourth write data based on third write data, adds a third guarantee code [to the fourth write data] and writes this data to the plurality of second storage devices and, if the second read command is received from the host computer, the controller reads third read data from the plurality of second storage devices, divides this data into fourth read data, and adds a fourth guarantee code and transmits the data to the host computer