Patent ID: 8473709

Claim:
A computer system comprising a computer and a storage device connected to the computer, wherein: the storage device has a volume for storing data of the computer and virtual volumes formed by logically dividing the volume; the computer has an arithmetic unit, a memory unit, a virtual computer operating on the arithmetic unit which is controlled by a virtualization mechanism, and volume management information for managing a status of use of the virtual volume and positional information on the virtual volume; the virtualization mechanism has a virtual volume allocating unit that allocates a new virtual volume to the virtual computer when a request for virtual volume allocation is received; the memory unit has virtual volume information for managing virtual volumes allocated to the virtual computer; and the virtual volume allocating unit references the volume management information and searches for any unused area in the volume, allocates a new virtual volume to an unused area in the volume if the unused area of the volume satisfies a size requirement for the virtual volume designated by the request for virtual volume allocation, updates the status of use of the virtual volume and positional information on the virtual volume that the volume management information has to a state after the allocation of the new virtual volume, and adds information on the new virtual volume to the virtual volume information.