Defrag decision

Q I downloaded the special offer program Uniblue Disk Rescue 2009 from Computeractive. I followed all the instructions and activated my copy.

When I came to scan the PC I got a message advising me not to continue as my operating system was protected by the Microsoft Volume Shadow Service. What is this and how can I use the defragmentation program?

Phil Chappell

A The Volume Shadow Service, or VSS, is a part of Windows that makes copies of your files so that if you change them you can still get back to the old versions, should you need to. It is used primarily by a tool called Shadow Copy, which is built into some versions of Windows Vista.

The shadow copy service is sometimes called Previous Versions. This allows you to access old version of files. Suppose you create a Word document and save it, then change it and save the changes over the top of the original document, but then decide you want to go back to the original. Previous Versions allows you to easily get the old document back, and it uses VSS to do it.

What happens when you defragment a hard disk is that the computer moves all the files, and parts of files, around on the physical disk surface, to make them more efficient. When it does this, VSS interprets each movement as a change to a file, and tries to record the previous version. That will make your hard disk fill up extremely rapidly, which is why it’s a bad idea to use a defragmenter if VSS is running.

If you wish to use the Uniblue product the only thing to do is to turn off the Previous Versions but it will mean also turning off System Restore, as in Vista the two are closely linked. You can, of course, turn it back on afterwards, but bear in mind that you may lose previous restore points even if you do so. A simpler answer might be to use a defragmenter that’s compatible with VSS. One such program that we’ve come across of is Auslogics Disk Defrag.

If you do want to turn off Previous Versions, though, here’s how: open the Control Panel from the Start menu. Click “System and Maintenance”, then click System, then click the System Protection link.

You may be asked to confirm what you’re doing, so click OK if you are. Then you’ll see a list of the disks on the PC with a tick box next to each indicating whether or not VSS is running on that disk – untick the box for each disk you want to defragment.

You’ll be asked to confirm whether to turn it off. When you’re done, click OK to close the dialogue box. You may need to restart the PC before defragmenting the disk, and don’t forget to reverse the process above to turn everything back on afterwards.