First it may be worthhile knowing how System Restore works

System Restore takes snapshots of your registry and other configuration data at odd intervals (not daily but almost) and before various operations, such as installing Windows updates. These are called Restore Points. If a problem occurs at some time and you can't find its cause, you can revert back to the restore point and restore your system to the time before the problem event. Volume Shadow Copy Service (VSSA) is the Windows device that carries out this function and works mainly in the background.

To make adjustments to the volume used by System Restore you will need to use the VSSA command-line tool. To do this, launch the Command Prompt in Start//Accessories. (If you have to run as Administrator right click the Command Prompt shortcut and select "Run as Administrator").

To obtain a list of all the restore points currently saved, enter this command at the insert point. (Blinking curser).

vssadmin list shadows

There is probably nothing you need to do with this information as it will change when you allocate the custom space for System Restore as shown below.
First take a look at how much disk space is currently allocated with the command:

vssadmin list shadowstorage

You will proably find it is taking rather a large slice out of your hard-drive, maybe 30/50 GB. To reset the Maximum Shadow Copy Storage space, enter this command:

vssadmin resize shadowstorage /for=<Enter the drive letter - Probably 'C'> /on=<Enter the drive letter - Probably 'C'> [/maxsize=<Enter the space you can afford. Say 10GB>

so it will look like this:

vssadmin resize shadowstorage /for=c: /on=c: /maxsize=10GB

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