Patent ID: 7657707

Claim:
A data processing method in a data storage system comprising: a processing unit, a first storage system coupled to said processing unit: and a second storage system coupled to said first storage system, said method comprising the steps of: (a) storing first write data received from said processing unit in a first cache memory of said first storage system, (b) reporting, to said processing unit, first completion of having written said first write data to said first cache memory of said first storage system, (c) storing, after receiving second write data from said processing unit which sent said second write data after receiving said first write data, said second write data in said first cache memory of said first storage system, (d) reporting, to said processing unit, second completion of having written said second write data to said first cache memory of said first storage system, (e) transmitting said first write data and first information regarding said first write data to said second storage system after reporting, to said processing unit, said first completion, (f) transmitting said second write data and second information regarding said second write data to said second storage system after reporting, to said processing unit, said second completion, (g) reporting, by said second storage system, a third completion of having written said first write data to a second cache memory of said second storage system after storing said first write data in said second cache memory of said second storage system, (h) sending, by said first storage system, a message to said second storage system after receiving said third completion from said second storage system, said message including information for destaging said first write data, and (i) destaging, by said second storage system, said first write data according to said message after receiving said message from said first storage system.