Patent ID: 8370573

Claim:
A computer system, comprising: a first storage system coupled to a host computer; and a second storage system coupled to the first storage system, wherein the first storage system includes a plurality of first physical disks, and a first disk controller for controlling to read/write data from/to the plurality of first physical disks; the second storage system includes a plurality of second physical disks, and a second disk controller for controlling to read/write data from/to the plurality of second physical disks, wherein the first disk controller is configured to provide a first thin provisioning logical volume (LU) to the host computer, wherein the second disk controller is configured to provide an external thin provisioning LU, associated with pool areas including a second internal LU provided by storage areas of the second physical disks, to the first storage system, wherein pool areas associated with the first thin provisioning LU include the external thin provisioning LU and a first internal LU provided by storage areas of the first physical disks, wherein the first disk controller is configured to: allocate, in response to receiving a first write request, a first pool area of the first internal LU to a first region in the thin provisioning LU which the first write request specifies, store data related to the first write request in the first storage area corresponding to the first pool area, and allocate, in response to receiving a second write request, a second pool area of the external thin provisioning LU to a second region in the thin provisioning LU which the second write request specifies, and transmit a third write request related to the second write request to the second storage system, wherein the second disk controller is configured to: allocate, in response to receiving the third write request, a third pool area of the second internal LU to a third region in the external thin provisioning LU which the third write request specifies; and store data related to the third write request in the third storage area corresponding to the third pool area.