1. A method for reconstituting a virtual snapshot of files in a file virtualization system, the method comprising: forming at a file virtualization device a virtual snapshot comprising a plurality of physical snapshots associated with one or more file storage devices participating in the virtual snapshot; receiving a request for performing an operation on one or more physical snapshots in the plurality of physical snapshots; providing the one or more physical snapshots in response to the request for performing the operation when the one or more physical snapshots exists in the virtual snapshot; and reconstituting the virtual snapshot by including the one or more physical snapshots to form a reconstituted virtual snapshot in response to the request for performing the operation when the one or more physical snapshots do not exist in the virtual snapshot.