Patent ID: 8407517

Claim:
A system comprising: a first storage system including: a first port to receive I/O operations from host computers; a first storage controller including a first processor and first memory; and a plurality of first storage devices, which stores data received from said host computers, and a second storage system including: a second port to receive I/O operations from said host computers via said first storage controller; a second storage controller including a second processor and second memory; and a plurality of second storage devices, which stores data received from said host computers, wherein error check codes corresponding to data stored in said plurality of second storage devices are stored in said first storage system, wherein, in response to I/O operations from said host computers to read data of a virtual volume, where the data are stored in said second storage system, check codes of the data stored are calculated and compared with corresponding error check codes for the data of the virtual volume and the corresponding error check codes are stored in said first storage system, and wherein, if the result of the comparison indicates that the check codes and corresponding error check codes match, the data stored in said second storage system are transferred to said host computers.