Patent ID: 7480814

Claim:
A network storage system coupled to a client computer via a network, comprising: a first node and a second node which provide the client computer with one or more file systems using one or more service IP addresses; an inter-node communication path which couples the first node and the second node to each other; and at least one disk subsystem coupled to the first node and the second node, wherein the disk subsystem has plural logical units, wherein at least one of the plural logical units is a shared logical unit which is used by the first node and the second node, wherein the first node includes: a priority recognizing processing module which consults a priority of a frame received from the client computer; a priority level determining processing module which determines, based on the priority of the frame, an order of fail over priority for plural software resources including the service IP address and the file system; and a first monitoring processing module which sends given monitoring signals at a given timing, wherein the priority level determining processing module: calculates a first value obtained by multiplying the priority by the number of frames that are received by the first node; calculates a second value which is the product of the square of the priority and the number of frames that are received by the first node; determines the order of fail over priority from the sum of the first value and the second value; and stores the determined order of fail over priority in the shared logical unit, and wherein the second node includes: a second monitoring processing module which receives the monitoring signals sent from the first monitoring processing module and, when the monitoring signals fail to arrive at the given timing, judges that a failure has occurred in the first node; and a fail over processing module which, when the second monitoring processing module judges that a failure has occurred in the first node, consults the order of fail over priority stored in the shared logical unit and performs fail over on the plural software resources according to the order of fail over priority consulted.