The present invention allows a back-up site used for disaster recovery to be constructed in a shorter period of time.In a disk array device 1 at a main site, a copy 4 of a RAID group 3 is generated. In-frame mirroring is used to generate this copy. The RAID group 4 is removed from the disk array device 1 by an operator and transported to a back-up site. The operator then installs each of the disks of the RAID group 4, respectively, in the disk array device 2, in such a manner that they adopt the same positions as in the RAID group 3. The configuration information 5 used in order to manage the RAID group 3 is downloaded to the disk array device 2 in the back-up site, by means of a portable storage medium 8, or via a communications network 7. Thereupon, the differential data between the disk array devices 1, 2 is reflected in the disk array device 2, whereupon construction of the back-up site is complete.