An embodiment of this invention is an information storage system comprising a plurality of storage systems connected to be able to communicate. Each of the plurality of storage systems includes default storage system identification information which is the same to the plurality of storage systems, common volume identification information for uniquely identifying volumes provided by the plurality of storage systems to a host computer among the plurality of storage systems, and a controller configured to return the default storage system identification information to the host computer in response to a request from the host computer and to process a read or write request to a volume accompanying the common volume identification information from the host computer.