According to this invention, in an environment in which are intermixed a plurality of storage subsystems with different processing performance, volumes are automatically relocated according to the state of use of each storage subsystem. A storage system comprises a plurality of storage subsystems 1, 2 with different processing performance. When unevenness occurs in the states of use of the storage subsystems 1, 2, and movement of a volume 2A becomes necessary, a management server 3 issues an instruction for volume movement to the copy source system 2 and to the copy target system 1 (S1). The management server 3 notifies a service-providing server 4 of the volume movement (S2). At the copy source, the volume 2A is allocated to a dummy volume 2B (S3), and at the copy target, an unused volume 1C is allocated to a dummy volume 1B (S4). Then volume copying is executed, and the volume is moved between the storage subsystems 1, 2.