Patent ID: 7334106

Claim:
An allocation method for allocating a plurality of logical volumes to form a plurality of virtual volumes among a plurality of virtualization switch apparatuses, the virtualization switch apparatuses being coupled to a plurality of host computers and to a storage device, the logical volumes related to at least one disk drive in the storage device, the virtual volumes processing input-output requests from the host computers, the method comprising steps of: issuing, to the plurality of virtualization switch apparatuses, a request for completing all input-output requests received from the host processors that are being processed by the virtualization switch apparatuses and temporarily holding any subsequent input-output requests received from the host processors; receiving, from the plurality of virtualization switch apparatuses, a completion report of the input-output requests being processed by the virtualization switch apparatuses in response to the request for completing; sending an instruction of an allocation change of logical volumes to all the virtualization switch apparatuses upon receiving completion reports from all the virtualization switch apparatuses to which the request for completing was issued; receiving a completion report of the allocation change from all the virtualization switch apparatuses; and sending an instruction to all the virtualization switch apparatuses for releasing the input-output request that are being temporarily held, wherein a virtualization switch apparatus that did not send its completion report is removed from a control range and the allocation of its logical volumes is not changed.