The storage system includes page area association information that associates a page area that partitions a storage area in a real volume into predetermined storage areas with a page area that partitions a storage area in a virtual volume into predetermined storage areas; a pair setting unit for pairing a primary virtual volume that stores data from a host computer and a secondary virtual volume to store a copy of the data stored in the primary virtual volume; and a page release unit for releasing association between a page area in the secondary virtual volume and a page area in the secondary real volume associated in advance with the page area in the secondary virtual volume.