Provided is a technology in which: a request-source storage device provides a request-source server device with a storage area of a disk drive as at least one logical volume; the request-source server device determines, upon receiving a request to back up data stored in a first logical volume, whether a second logical volume which constitutes a copy pair with the first logical volume is present in the request-source storage device; the request-source server device requests, upon determining that the second logical volume is not present, the request-source storage device to produce the second logical volume; and the request-source server device transmits a request to execute a process to back up data stored in the existing or produced second logical volume to the backup storage device to the request-destination server device. Accordingly, data to be stored in a NAS not locally coupled to a backup device is appropriately backed up.