Patent ID: 7216208

Claim:
A system for storing data comprising: a first storage system coupled to a processing unit, said first storage system comprises first disk units and a first controller; and a second storage system coupled to said first storage system, said second storage system comprises second disk units, a second controller, and a second cache memory, wherein said first controller receives write data from said processing unit, stores the received write data in a first disk unit, and transmits the received write data and reference information to said second controller, and wherein said second controller selects write data not to be stored in a second disk unit from write data being stored in said second cache memory according to the received reference information, and scraps the selected write data, wherein said second controller stores the received write data to said second cache memory, and selects write data to be stored in a second disk unit from write data being stored in said second cache memory according to the received reference information, wherein said second controller scraps the selected write data not to be stored in a second disk unit, when said first storage system is broken.