Patent ID: 8127102

Claim:
A storage system comprising: a primary storage apparatus including plural hard disks for storing data sent from a host computer, forming at least one real volume with the plural hard disks and providing a primary virtual volume to which a storage area of a real volume of the at least one real volume is dynamically allocated in response to a write request from the host computer; and a secondary storage apparatus connected to the primary storage apparatus providing a secondary virtual volume for storing copy data sent from the primary virtual volume, wherein the primary storage apparatus checks whether or not the storage area is allocated to each primary slot area formed by partitioning a storage area in the primary virtual volume into predetermined storage areas when the primary virtual volume and the secondary virtual volume are paired, wherein if no storage area is allocated to the primary slot area, the primary storage apparatus sends a notice indicating no data is stored to the secondary storage apparatus, wherein when the notice is received from the primary storage apparatus, the secondary storage apparatus writes zero data in the secondary slot area, and wherein if the storage area of the real volume is not allocated to the primary slot area, the secondary storage apparatus writes no zero data to the secondary slot area related to the primary slot area included in the notice, and if the storage area of the real volume is allocated to the primary slot area, the secondary storage apparatus writes zero data in the secondary slot area related to the primary slot area included in the notice.