Each communication path between controllers and a plurality of storage devices has a plurality of expanders coupled in series. In order to shorten the time during which the communication path is not used for I/O, either (A) the length of time for which I/O suppression is set for the communication path is shortened, or (B) the overall time it takes for processing other than I/O processing is shortened. In the (A), a determination as to whether or not the coupling between the expanders has been disconnected is made for the I/O-suppressed communication path, and in a case where the result of this determination is negative, a discover process is carried out after releasing the I/O suppression with respect to this communication path. In the (B), the number of command issue times of updating routing control information of the expander is reduced.