Patent ID: 7424582

Claim:
A storage system comprising: a host system; a first storage sub-system including at least one first physical storage device and a first storage controller connected to the host system and directly connected with said first physical storage device to exercise an exclusively control thereon; and a second storage sub-system including at least one second physical storage device and a second storage controller connected to the first storage controller and directly connected with said second physical storage device to exercise an exclusively control thereon, wherein the first storage controller further comprises: a first controller configured to virtualize a storage area located in said second physical storage device and exclusively controlled by the second storage controller and provide a virtualized storage area as if internally controlled by the first storage controller to the host system; a memory configured to store format identifying information for the storage area; and a second controller configured to designate, when receiving a request for formatting of the storage area, the second storage controller to format the storage area based on the format identifying information stored in the memory, and wherein the format identifying information is information for identifying either as first formatting that designates the second controller to transmit only a first write command for writing control information to said second storage controller which then writes said control information into a control information area in the storage area, or as second formatting that designates the second controller to transmit a second write command for writing data of value 0 to said second storage controller which then writes said data of value 0 into a user data area in the storage area, and to transmit the first write command to said second storage controller which then writes said control information into the control information area in the storage area.