Patent ID: 7203814

Claim:
An allocation method for a storage area of a storage device to a virtual volume in a storage system having a plurality of virtualization apparatuses that allocate the storage area which the storage device has, form a plurality of virtual volumes, and process input-output from a host processor to one of the virtual volumes, comprising the steps of: issuing, to the plurality of virtualization apparatuses, a request for completing all input-output requests received from the host processors that are being processed by the virtualization apparatuses and temporarily holding any subsequent input-output requests received from the host processors; receiving, from the plurality of virtualization apparatuses, a completion report of the input-output requests being processed by the virtualization apparatuses in response to the request for completing; sending an instruction of an allocation change of the storage area of the storage device to all the virtualization apparatuses upon receiving completion reports from all the virtualization apparatuses to which the request for completing was issued; receiving a completion report of the allocation change from all the virtualization apparatuses; and sending an instruction to all the virtualization apparatuses for releasing the input-output request that are being temporarily held, wherein a virtualization apparatus that did not send its completion report is removed from a control range and the allocation of its storage area is not changed.