/Shadow=ShadowId /ForceDismount /Quiet - Reverts a volume to its state at the time of the shadow copy. All shadow copies ...

%1 %2 /Shadow=ShadowId [/ForceDismount] [/Quiet]
    - Reverts a volume to its state at the time of the shadow copy.  
    All shadow copies of the volume taken after that point will be
    removed.  All changes to files and folders on the volume made
    after the time of the shadow copy will be permanently lost.  
    The revert operation cannot be undone.  Once the revert 
    operation is started, it cannot be canceled.  If any handles 
    are currently held on the volume, the revert will fail unless 
    the ForceDismount flag is specified.  

    Example Usage:  vssadmin Revert Shadow 
                             /Shadow={c5946237-af12-3f23-af80-51aadb3b20d5}
                             /ForceDismount