Disaster recovery is being adopted in an increasing number of cases. Disaster recovery refers to a mechanism in which a copy of data used by an operation (for example, a virtual machine) performed at a first site (a first computer system) is created at a remote second site (a second computer system) and, upon loss of the data used by the operation, the copy of the data is used to continue the operation at the second site. Generally, data copying for disaster recovery is realized by remote copying that is performed as follows. Specifically, data stored in a copy source VOL (a primary VOL) owned by the first site is transferred to the second site and copied to a copy destination VOL (a secondary VOL) in the second site. “VOL” is an abbreviation of a logical volume. Generally, a pair is constituted by one copy source VOL and one copy destination VOL. When there are a plurality of copy destination VOLs with respect to one copy source VOL, a plurality of pairs can be created.
In addition, as an example of load balancing related to disaster recovery, at least one of the sites including the first and second sites conceivably has both a copy source VOL and a copy destination VOL. Specifically, for example, the first site includes a first copy source VOL and a second copy destination VOL. The second site includes a second copy source VOL which constitutes a pair with the second copy destination VOL (or a copy destination VOL of another site) and a first copy destination VOL which constitutes a pair with the first copy source VOL (or a copy source VOL of another site). Recently, there is an increase in corporations using a plurality of sites in order to retain continuity of operations and such environments have become commonplace.
Normally, in such an environment, an allocated resource amount to a copy source VOL is large while an allocated resource amount to a copy destination VOL is small enough to enable processing of remote copying (writing).
PTL 1 discloses a technique for migrating data while taking an association between VOLs into consideration.