Patent ID: 8458697

Claim:
A computer system, comprising: a first computer that executes a plurality of virtual machines; a storage device coupled to said first computer, including a storage medium; and a second computer, coupled to said first computer and to said storage device, that applies a patch to a virtual machine for an OS (operating system) operating upon said virtual machine; wherein said storage device comprises: a master logic unit, that is a storage region storing data at some time instant for said OS operating upon said virtual machine; a storage pool, that is a storage region storing the patch applied to said OS upon said virtual machine after said certain time instant; and a snapshot logic unit that stores data, that is data of said OS upon said virtual machine, and that is supplied from a snapshot acquired from said master logic unit, and from the patch stored in said storage pool; wherein said second computer holds management information, and said management information specifies a correspondence relationship between an identifiers of said virtual machine and an identifier of the patch applied to the OS of said virtual machine, and moreover specifies whether or not said patch applied to the OS of said virtual machine is stored in said storage pool; and said second computer: selects said master logic unit to which is applied a combination of patches that are made up from a combination of patches applied to the OS of a target virtual machine, that is one said virtual machine among said plurality of virtual machines, as a target master logic unit that is to be a source of acquisition of a snapshot of the snapshot logic unit that corresponds to said target virtual machine; refers to said management information; and performs duplication elimination in which a patch, among the patches applied to said target virtual machine, that is stored in said target master logic unit, and that moreover is stored in said storage pool, is deleted from said storage pool.