Patent US 7,313,722

A node 1 and a node 2 are in a mutual failover relationship and share information used in failover through a shared LU. Of filesystems FS1A, FS1B that are mounted at the node 1, the actions of level 1 are allocated to FS1A and the actions of level 2 are allocated to FS1B. The level 1 filesystem FS1A is taken over to the node 2 simultaneously with commencement of failover. The level 2 filesystem FS1B is taken over to the node 2 when an access request for FS1B is generated after commencement of failover. In this way, business services with high availability can be restarted at an early stage.