In a computer system wherein plural servers are connected with an external disk device via a network, each server incorporates therein a logic partition module for configuring at least one logic partition in the server, and the operating system stored in the logic partition is booted by the boot disk of an external disk device, the failover operation is performed only for the logic partition affected by a failure when the task being executed by a working server is taken over by another server at the time of the failure occurring in the working server.