1. A storage system coupled to a computer in which a plurality of virtual computers are operated, comprising a controller and a plurality of memory devices, wherein the storage system is configured to: store OS data in a first volume provided by the plurality of memory devices; and provide a plurality of first virtual volumes to which the first volume is allocated; wherein the plurality of virtual computers being operated using any one of OS images provided by each of the plurality of first virtual volumes; and wherein the controller is configured to: create a replication of the first volume storing the OS data when a patch applying request is received from the computer to at least two or more first virtual computers; create a second volume by applying a patch having received the patch applying request to the replicated volume; generate a plurality of second virtual volumes to which the second volume is allocated; and switch the allocation of each of the first virtual computers from the first virtual volumes to any one of the plurality of second virtual volumes.