Need command prompt running with elevated privilege.
Default usage settings should be 15% Total Disk Space or 30% Available Disk Space, whichever is less. 1GB minimum.
To display current usage:
C:>\vssadmin list shadowstorage
If Maximum Shadow Copy Storage apace:UNBOUNDED
This is a bad thing. You will get Low Disk Space warnings
To set usage appropriately, consider this example:
C:>\vssadmin resize shadowstorage /for=c: /on=c: /maxsize=50GB