Following command can be used to add a shadow copy storage association for a specified volume:
vssadmin add shadowstorage /for=
Example,
To specify that for volume C and volume D is to be used for storage and the maximum size for storage space is to be 900 MB, type:
vssadmin add shadowstorage /for=c: /on=d: /maxsize=900mb
For more information please refer to Microsoft Documentation : https://technet.microsoft.com/en-us/library/cc788051(WS.10).aspx
Acknowledgement : Microsoft