A controller 2 uses a virtual logical volume 3 having an expandable volume size to perform either a remote copy or an internal copy without suspending access from a host. The virtual logical volume 3 is able to expand a volume size in units of a cylinder group 6 that have a size equivalent to 25 pages. Information for managing a copy is stored in a control area 6B inside the cylinder group 6. This enables storing of copy management information in accordance with the expanded size of the virtual logical volume.