Patent ID: 7203807

Claim:
A storage system coupled to an upper device and to another storage system, comprising: a first circuit arranged to receive a write request from said upper device; a first logical volume arranged to store data included in said write request; and a second circuit arranged to transmit data in said first logical volume to a second logical volume of said another storage system; wherein said first logical volume and said second logical volume have a pair relation in which asynchronous data are duplicated; wherein said storage system is arranged to receive a query on information regarding data written into said second logical volume in said another storage system, said query being transmitted from said upper device; make a query on the information regarding data written into the second logical volume of said another storage system, via said second circuit; receive the information regarding data written into the second logical volume, which is transmitted from said another storage system via said second circuit; and transmit the received information to said upper device, and wherein the pair relation between said first logical volume and said second logical volume is a relation in which said first logical volume is a main logical volume and said second logical volume is a logical sub-volume, and the information regarding data written into the second logical volume is information representing the sequence of data written into said second logical volume.