The storage system includes a disk controller for receiving write commands from a computer, and a plurality of disk devices in which data is written in accordance with the control of the disk controller. The size of the first block which constitutes the data unit handled in the execution of the input/output processing of the data in accordance with the write command by the disk controller is different from the size of the second block which constitutes the data unit handled in the execution of the input/output processing of data by the plurality of disk devices. The disk controller issues an instruction for the writing of data to the disk devices using a third block unit of a size corresponding to a common multiple of the size of the first block and the size of the second block.