1. A storage system, comprising: a secondary storage; a channel interface coupled to a server; a disk interface coupled to the secondary storage; a cache memory for temporarily storing data to be sent to and received from the secondary storage; and a processor; wherein a swap area of a main memory of the server is allocated to the secondary storage; wherein the processor refers to data stored in the secondary storage and specifies the swap area, stores the specified swap area in the cache memory, and sends data of the swap area of the cache memory to the main memory of the server; wherein a host OS of the server runs a plurality of virtual machines; wherein the secondary storage stores a plurality of virtual machine files storing the respective statuses of the plurality of virtual machines; wherein each of the virtual machine files comprises a status unit showing the setting of the virtual machines and the execution status of programs, and an image unit as data of the secondary storage to which the virtual machines are virtually coupled, wherein the image unit includes a guest OS for running the virtual machines, and the guest OS includes a swap area for the guest OS to perform swap processing; and wherein the processor determines a file system of the host OS; searches for the virtual machine files based on the determined file system; determines virtual machine software of the searched virtual machine files; selects a virtual machine analysis program corresponding to the determined virtual machine software; specifies the image unit of the virtual machine files based on the selected virtual machine analysis program; specifies the swap area of the guest OS from the specified the image unit; and causes the specified swap area to reside in the cache memory.