An information processing system having a storage apparatus and a file sharing server. The storage apparatus comprises a plurality of storage devices for providing logical devices to store data; and a first processing unit for providing virtual logical units based on a mapping relation between the logical devices and the virtual logical units and being operative to switch the mapping relation dynamically according to an external request. The file sharing server comprises a cache memory including cache extents and a second processing unit controlled to provide the virtual logical units of the storage apparatus to a host system by using the cache extents, managing the mapping relation between the logical devices and the virtual logical units. The mapping between a logical unit and a logical device is dynamically switched as the logical devices store data provided from the host system according to external requests.