1. A storage system coupled to a computer in which a plurality of virtual computers is 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 is operated using any one of OS images provided by each of the plurality of first virtual volumes; 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 of the plurality of the 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 plurality of the first virtual volumes to any one of the plurality of second virtual volumes; wherein the replication of the first volume is performed by having the data stored in the first volume copied to a different volume or by having a new virtual volume associated with the first volume created; wherein, when the allocated plurality of the second virtual volumes in a second virtual computer has difference data regarding the OS data stored in the first volume, switching is not performed for the second volume allocated to the second virtual computer, wherein a replication of the first volume is created when a request to execute a test with respect to the second virtual computer is received; wherein, following receipt of the patch applying request, a patch is applied to the replication of the first volume; wherein a test volume is created by applying difference data stored in the first virtual volume allocated to the second virtual computer; and wherein a notification is made as to a result of performing the test so as to determine whether or not the test volume has a problem.