Patent ID: 7634626

Claim:
A remote copy system comprising: a plurality of primary storage systems, wherein each of the plurality of primary storage systems comprises a first controller and a source logical volume coupled to said first controller; and a plurality of secondary storage systems, wherein each of the plurality of secondary storage systems comprises a second controller, a memory, a cache memory and a target logical volume storing copy data of a primary logical volume, wherein the first controller of each of said primary storage systems comprises: a write-data receiving unit that receives write data from a host computer and creates, for the write data received from the host computer, write-data management information including sequential numbers and section numbers, the sequential numbers being based on an order of receiving the write data; and a write-data transfer unit that creates write data information with reference to the write-data management information, and sends to one of said plurality of secondary storage systems the write data and corresponding write-data information, which includes the sequential numbers and the section numbers, and wherein the second controller of each of said secondary storage systems comprises: a write-data receiving unit that receives the write data and the write-data information from a primary storage system of the plurality of primary storage systems and stores the write data and the write-data information received from the primary storage system in the cache memory, creates write-data management information from the write-data information received, determines a largest section number value from among the section numbers included in the write-data information stored in the cache memory, stores the largest section number value in the memory, compares the largest section number value stored in the memory with a value of a section number of the received write-data information, and updates the largest section number value stored in the memory with the value of the section number of the received write-data information when the value of the section number of the received write-data information is greater than the largest section number value stored in the memory; and a write-data reflecting unit that obtains a smallest section number value from among the write-data information stored in the cache memory by the write-data receiving unit for the target logical volume, wherein one said second controller of said plurality of secondary storage systems obtains the section numbers stored in each said memory of each of the plurality of secondary storage systems and commands all of the plurality of secondary storage systems to reflect the write data having section number values smaller than the smallest section number value obtained by the write data reflecting unit to the target logical volume, in an order of the sequential numbers.