Patent ID: 8572316

Claim:
A storage system comprising: a first storage system coupled to a computer; and a second storage system coupled to the first storage system; wherein the first storage system includes: a plurality of first storage devices; and a first controller providing a thin provisioning logical volume (LU) to the computer; wherein the second storage system includes: a plurality of second storage devices; and a second controller providing an external thin provisioning LU to the first storage system; wherein the first controller is configured to: provide pool areas, which are associated with the thin provisioning LU, including a first pool area mapped to the external thin provisioning LU, and, allocate the first pool area to a first region in the thin provisioning LU to store a write data to the first region in the thin provisioning LU from the computer; and wherein the second controller is configured to allocate at least one of a plurality of external pool areas, which are provided by at least one of the second storage devices, associated with the external thin provisioning LU to store the write data to the first region in the thin provisioning LU.