The following steps are performed in a storage system: when volumes configuring
each volume pair are used by separate applications, storing, for each pair in a
memory, an address where updating of data has been made in the volumes as updated-location-managing
information; in case a destination-of-restoring copy volume configuring one pair
is to be restored to have the contents of a source-for-restoring copy volume belonging
to another pair, obtaining, from the memory, pieces of the updated-location-managing
information for each of the pairs; generating differential information by merging
the pieces of updated-location-managing information obtained, the differential
information indicative of a difference in the pieces of updated-location-managing
information between the copy volumes; and reproducing the destination-of-restoring
copy volume to have the contents of the source-for-restoring copy volume, by copying
data designated by the differential information from the source-for-restoring copy
volume to the destination-of-restoring copy volume.
