Patent ID: 7617227

Claim:
A storage control sub-system coupled to a host terminal via a storage area network (SAN) and coupled to a management terminal, the storage control sub-system comprising: a plurality of physical storage devices; and a storage control section managing a plurality of logical storage devices comprising a first logical storage device, which is prepared from a first plurality of physical storage devices of said plurality of physical storage devices, and a second logical storage device, which is prepared from a second plurality of physical storage devices of said plurality of physical storage devices; wherein said storage control section manages a logical storage unit being provided to the host terminal after allocating to said first logical storage device, wherein said storage control section manages a virtually logical storage unit which is configured from a plurality of virtual storage regions and is provided to the host terminal without being allocated to said second logical storage device by establishing a virtual storage capacity value, wherein said storage control section manages a first Redundant Array of Inexpensive Disks (RAID) group of the first plurality of physical storage devices, and manages a second RAID group of the second plurality of physical storage devices, and receives a write request from said host terminal, wherein said storage control section controls to write data of said write request in a storage area of said first logical storage device which is already allocated to the logical storage unit, if said write request is targeted to said logical storage unit, wherein said storage control section controls to allocate a storage area of said second logical storage device and controls to write said data of said write request in said allocated storage area of said second logical storage device, if said write request is targeted to said virtually logical storage unit, wherein said storage control section receives a request for changing said virtual storage capacity value of said virtually logical storage volume from the management terminal, wherein said storage control section controls to reject said request for changing said virtual storage capacity value of said virtually logical storage volume, if said virtual storage capacity value of said virtually logical storage volume is already reported to the host terminal, and wherein said storage control section controls to change said virtual storage capacity value of said virtually logical storage volume based on said request for changing said virtual storage capacity value of said virtually logical storage volume, if said virtual storage capacity value of said virtually logical storage volume is not reported to the host terminal yet.