Patent ID: 7590818

Claim:
A storage system, comprising: a plurality of storage devices coupled to a computer, each storage device accessing data from/to said computer, wherein each storage device includes: a plurality of logical volumes for storing data, a plurality of virtualization devices allocating said logical volumes to form a plurality of virtual volumes, and to process input-output requests sent from said computer to one of the virtual volumes, and a copy control unit migrating data in at least one of said plurality of logical volumes, wherein said copy control unit is operable to copy data while permitting input-output requests from said computer to at least one of said plurality of virtual volumes as a copy source volume, and wherein, if at least one of said plurality of storage devices receives an input-output request from said computer during said copy of data, said at least one of the plurality of storage devices holds said input-output request until said copy control unit completes the copying so that data corruption as a result of the input-output request is prevented, wherein at least one of said plurality of storage devices is operable to perform steps comprising: issuing, to each of said plurality of virtualization devices, a request for completing all input-output requests received from said computer that are being processed by said virtualization devices and temporarily holding any subsequent input-output requests received from said computer; receiving, from the plurality of virtualization devices, completion reports of the input-output requests being processed by said virtualization devices in response to said request for completing; sending an instruction of an allocation change of a storage area to all said virtualization devices if all of the completion reports from all said virtualization devices are received; receiving completion reports of the allocation change from said virtualization devices; and sending an instruction to said virtualization devices for releasing the input-output requests that are being temporarily held.