To provide a storage system partitioned into logical partitions. A storage system includes: a plurality of disk drives; and a disk controller that is connected to the disk drives and reads/writes data from/into the disk drives, wherein the disk controller includes: a disk control unit that exchanges data with the disk drives; a channel control unit that exchanges data with another computer; a switch unit that is connected to the disk control unit and the channel control unit and exchanges data therewith; and a control unit that controls the disk control unit, the channel control unit, and the switch unit, and wherein the disk controller is partitioned into a plurality of logical partitions, the control unit controls the partitioning into the logical partitions, and the switch unit controls a data transmission band width of each logical partition by obtaining, for each piece of data to be exchanged, information indicating a logical partition to which the data belongs, and arbitrating data transmission for the logical partition.