/For=ForVolumeSpec|/On=OnVolumeSpec - Displays all shadow copy storage associations on the system. To list all associations ...

%1 %2 [/For=ForVolumeSpec|/On=OnVolumeSpec]
    - Displays all shadow copy storage associations on the system.    
    To list all associations for a given volume, specify a 
    ForVolumeSpec and no /On option.  To list all associations on a given 
    volume, specify an OnVolumeSpec and no /For option.

    Example Usage: vssadmin List ShadowStorage /On=C: