Patent ID: 8145842

Claim:
A computer system, comprising: a first storage system coupled to a host computer and including a plurality of first physical disks for storing data requested to write by the host computer and a first disk controller for controlling to read/write data to the plurality of first physical disks; and a second storage system coupled to the first storage system and including a plurality of second physical disks for storing data requested to write by the first disk controller and a second disk controller for controlling to read/write data to the plurality of second physical disks, wherein the first disk controller is configured to: provide a first external logical volume, which is a real volume constituted by storage area of the second physical disks, to the host computer; and further provide a thin provisioning logical volume to the host computer, wherein a first storage pool is assigned to the thin provisioning logical volume, wherein the first storage pool includes a second external logical volume, which is a real volume constituted by storage area of the second physical disks, and wherein at least one of a plurality of storage areas of the first storage pool is allocated to the thin provisioning logical volume when a write request to the thin provisioning logical volume is received from the host computer.