Patent ID: 8595436

Claim:
A computer system coupled to a host computer and a management server, the computer system comprising first, second and third storage systems which are each separate from and do not include the management server or the host computer, wherein the first storage system and the second storage system each are coupled to the host computer and the management server and each comprise a virtual storage system for the host computer, wherein the first storage system is coupled to the host computer without the second storage system being interposed between the first storage system and the host computer, and wherein the second storage system is coupled to the host computer without the first storage system being interposed between the second storage system and the host computer, the first and second storage systems each including a command-function correspondence table having first correspondence information regarding correspondence relationships between commands from the host computer and functions of the first and the second storage systems and a function-device correspondence table having second correspondence information regarding correspondence relationships between the functions and the storage systems that have the functions, wherein the third storage system is coupled to the first storage system and the second storage system and comprises a real storage system for the first and second storage systems, wherein one of the first and the second storage systems is configured to provide a logical volume of the third storage system as a virtual volume to the host computer, wherein the host computer is configured to recognize the first and the second storage systems logically as a single virtual storage system, and wherein one of the first and the second storage systems is configured to: receive a command from the host computer to the virtual storage system; determine which of the storage systems possesses the function corresponding to the command by referring to the first and second correspondence information; if said one of the first and the second storage systems has possession of the function, execute the command; and if said one of the first and the second storage systems does not have possession of the function, transfer the command to the other one of the first and the second storage systems in possession of the function corresponding to the command by referring to the second correspondence information.