Patent ID: 7472239

Claim:
A storage system having first and second storage apparatuses, and which duplicates and retains data written by a host system into a first volume in said first storage apparatus by copying said data to a second volume in said second storage apparatus, wherein said first storage apparatus comprises a processor for allocating a storage extent of said first volume to a virtual volume when said first storage apparatus receives a write request to the virtual volume from said host system, said first volume is pair-configured with said second volume, for sending data written by said host system into said first volume further into said second volume, and for performing a processing to write data of value 0 in an address position in said second volume corresponding an address position in said first volume that has not been allocated to the virtual volume, and wherein said second storage apparatus comprises a processor for writing said data sent from said first storage apparatus into an address position in said second volume corresponding to an address position in said first volume that has been allocated to the virtual volume.