Patent ID: 7269646

Claim:
A cluster storage system comprising: a first storage node and a second storage node, each of which has at least one disk and a processor for controlling an access to said at least one disk; a host interface node for receiving an access request for a logical device from a computer and forwarding the access request to either said first storage node or said second storage node in accordance with the access request; and an internal network for interconnecting said first storage node, said second storage node and said host interface node, wherein one of said first storage node and said second storage node manages a first storage area existing on the disk in said first storage node and a second storage area existing on the disk in said second storage node as a single logical device, wherein said host interface node, in response to an access request having identification information corresponding to said logical device received from said computer, forwards the access request to a storage node which manages said logical device based on the received access request, wherein said storage node which manages said logical device, in response to the access request received thereby, determines whether a storage area to be accessed is included in said first storage area or said second storage area, and forwards the access request to the other storage node when the storage area to be accessed does not belong to the storage area in said storage node which manages said logical device, wherein said first storage node manages said first storage area belonging to said first storage node as a first physical device, wherein said second storage node manages said second storage area belonging to said second storage node as a second physical device, and said second storage node manages said second physical device as a second lower logical device, wherein said first storage node manages said second lower logical device as a first virtual device, and said first storage node manages a storage area having said first physical device and said first virtual device as a first lower logical device, wherein said host interface node manages said first lower logical device as an upper logical device, wherein said host interface node, in response to an access request having identification information of said upper logical device received from said computer, transmits an access request for said first lower logical device to said first storage node, and wherein said first storage node, in response to an access request for said first lower logical deice received from said host interface node, transmits an access request for said second lower logical device corresponding to said first virtual device to said second storage node when a storage area to be accessed belong to the storage area in said second storage node.