Regardless of which of the multiple storage subsystems provided with the same identification information is accessed from a plurality of host computers, multiple volumes provided with the same identification information among the storage subsystems are subjected to extent exclusion sharing. Therefore, a multiplex volume provided with the same identification information among the plurality of storage subsystems and a first storage subsystem for processing input/output requests by the channel command to the multiplex volume are provided, wherein if the channel command received from the host computer or via a control unit of a second storage subsystem is an input/output request of the multiplex volume, a control unit of the first storage subsystem determines the access authority regarding an extent range of the multiplex volume designated by the channel command, based on information on whether an input/output processing regarding the extent range is already executed based on another request.