Storage system and load balancing method thereof

Provided is a computer system having a host computer that requests the input and output of data in and from an actual storage volume, and a plurality of storage subsystems respectively having at least one or more virtual storage volumes. The virtual storage volumes of each of the plurality of storage subsystems are virtualizations of a common external volume. The host computer sets a certain logical path among a plurality of logical paths to be respectively connected to a plurality of virtual storage volumes formed by virtualizing the common external volume as an alternate path of another logical path.