Patent ID: 8086796

Claim:
A storage system comprising: a host computer; and a plurality of storage subsystems each for providing a storage space to the host computer, wherein the host computer comprises: a first memory part for storing therein first management information in which a virtual disk for making the storage space in a plurality of the storage subsystems as a virtual disk, a space on the virtual disk, a logical disk to which the virtual disk outputs a data, and load information on the logical disk are associated with each other; and a virtual disk control part for controlling an input/output request into the virtual disk, wherein a plurality of the storage subsystems comprises: a second memory part for storing therein second management information in which the logical disk, a space on the logical disk corresponding to the space on the virtual disk, and load information on the logical disk are associated with each other; and a load monitoring part for measuring load on the logical disk by the input/output request and storing the measured load in the second management information as load information, and wherein the virtual disk control part determines, if an input/output request into the virtual disk is performed, whether or not a space on a virtual disk specified by the input/output request is a not-ever-outputted space into which a data has not ever outputted, according to a determination whether or not the logical disk is assigned to a space on the virtual disk in the first management information, identifies, if the input/output request is to be performed to the not-ever-outputted space in which a logical disk is not assigned to the space on the virtual disk, a logical disk on the virtual disk based on the load information in the first management information, sends the input/output request to a storage subsystem having the identified logical disk, and updates, upon receiving a completion acknowledgement of the input/output request, the load information in the first management information based on the load information in the second management information.