For use in a system where a plurality of servers are connected to an external disk device, a method is provided for a server to boot an operating system from the external disk device. The method includes the steps of searching for the port of a network switch to which the server is connected; establishing a network to which only the server and a management server belong; sending a server information acquisition program from the management server to the server via a network boot operation; acquiring, by the server information acquisition program, unique information owned by the storage interface of the server for transfer to the management server; and setting, by the management server, a disk within the external disk device accessible from the server based on the unique information.