Patent ID: 7171517

Claim:
A storage apparatus comprising: a plurality of primary disk controllers each including a cache memory, each primary disk controller coupled to at least one disk device, said plurality of primary disk controllers being connected to at least one host computer; a secondary disk controller including a cache memory, said secondary disk controller being configured to receive data sent from the plurality of primary disk controllers by remote copy process; and a disk device connected to the secondary disk controller, wherein the cache memory of each primary disk controller has a first area for storing update data that are to be written to the corresponding disk device connected thereto, and a second area for storing overwritten update data that are to be transferred to the secondary disk controller, each primary disk controller receives said updated data sent from the host computer so as to be stored into the second area of the cache memory as said overwritten update data that are to be transferred to the secondary disk controller, transfers the stored overwritten update data to the secondary disk controller, and performs remote copying to the secondary disk controller, each primary disk controller overwrites said overwritten update data during at least one time period in the second area of the cache memory, records in said update data sent from the host computer overwrite corresponding records defined in said overwritten update data during the at least one time period such that the overwritten update data overwritten and stored during the time period are transferred to the secondary disk controller together, and the secondary disk controller handles the overwritten update data sent from the plurality of primary disk controllers as real data having consistency, wherein each of said plurality of primary disk controllers includes a cache memory and a control memory, each primary disk controller is configured to add timestamps and acceptance numbers to said update data sent from the host computer so as to be stored into the second area of the cache memory, and when a record is updated on the overwritten update data stored in the cache memory of each primary disk controller, information of the number of overwrites is stored in the control memory; and in the secondary disk controller, the overwritten update data is verified in accordance with the information of the timestamp, the acceptance number, and the number of overwrites.