Patent ID: 7360051

Claim:
A storage apparatus having a storage control device and a storage unit comprised of a plurality of physical storage devices, wherein the storage control device comprising: a control section for communicating with a host apparatus and the storage unit; a cache memory for storing temporarily data transferred between the host apparatus and the storage unit; and a shared memory in which control information communicated by the control section is stored, wherein the storage control device defines a logical device of an external storage unit set on a plurality of physical storage devices in at least one external storage apparatus each of which has an I/O processor and is connected outside a chassis of the storage apparatus as a logical device inside the storage apparatus, the storage control device maps a plurality of logical volumes of at least one RAID group accessible by the host apparatus to said logical device of an external storage unit, the storage control device relocates said logical volumes of at least one RAID group by moving data per logical device from one mapped logical device to a to-be-mapped logical device with a superior performance and re-mapping said logical volumes of at least one RAID group from said mapped logical device to said to-be-mapped logical device, and at least one of the mapped and to-be-mapped logical devices is said logical device of an external storage unit, the storage control device virtualizes the logical device of the external storage unit along with a logical device set on the plurality of physical storage devices in the storage apparatus, and provides the virtualized logical volume to the host apparatus, the storage control device issues I/O commands to both said logical device physically located therein and the logical device of the external storage unit, measures respective I/O occupied times based on a corresponding response time thereof, determines if the to-be-mapped logical device has a performance superior to the mapped logical device to trigger relocation, and determines whether the logical device therein or the logical device of the external storage unit is a relocation destination, if the to-be-mapped logical device has a performance superior to the mapped logical device, and if the logical device of the external storage unit is determined as the relocation destination, the storage control device virtualizes the logical device of the relocation destination and provides the virtualized logical device to the host apparatus.