The first controller includes a first relay circuit which is a circuit that controls data transfer, and a first processor coupled to the first relay circuit via a first second path. The second controller includes a second relay circuit which is a circuit that controls data transfer, and is coupled to the first relay circuit via the first path, and a second processor coupled to the second relay circuit via a second second path. The first processor is coupled to the second relay circuit not via the first relay circuit but via a first third path, and accesses the second relay circuit via the first third path during an I/O process. The second processor is coupled to the first relay circuit not via the second relay circuit but via a second third path, and accesses the first relay circuit via the second third path during an I/O process.