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Third party disk management tools ? beware

08/07/09

Third party disk management tools ? beware

Permalink 12:37:26 pm by Eugene Gardner, Categories: General, Technical Tips

Since their recent publicity drive and incorporation of trial software free with some magazines, I have been asked about using Uniblue DiskRescue and other similar tools.

There is a potential problem relating to the Volume Shadow Service (VSS), part of Windows since XP SP2, that enables a snapshot or shadow copy of a file to be taken periodically. This can be handy if you make a change to a file then want to revert to a previous version ? it is this that allows a backup to be taken while normal work continues on the file being backed up, avoiding the delays that file locking used to introduce. It is also relied upon for System Restore to work and so is generally enabled.

The problem with defragmenting a disk with VSS enabled is that every block move may trigger a change and so rapidly fills up the disk with spurious ?old? versions of files. Moreover, this activity would slow a defragmentation exercise down to a crawl (not the fastest activity at the best of times).

Some defragmenters and backup softwares are aware of this and switch system restore and shadow copies off before they start, then on again at the end. They have to do more than this though as otherwise all previous restore points would be lost; so they have to make copies of all restore files and settings before and put them back after. This is not a trivial activity and it would be easy to trash the system if got wrong.

However, Microsoft (and a few others) have written their code to avoid this problem and so their defragmenter and backup program are safe to use.

The Uniblue program seems not to have taken such precautions. Also, it only works with 32 bit systems, not 64 bit ones (such as all those I specify for clients now). As System Restore is probably worth having, I suggest that it is left it on and the Uniblue (and other similar) defraggers avoided until this issue is confirmed as resolved.

The defragmenter that is bundled with Windows Vista is scheduled to run each week by default, it does not show a fancy graphical depiction of the disk but is otherwise sound. Similarly, the bundled backup software is fine for most basic backup tasks. Be wary about using other software ? especially freeware, from authors without the resources to implement and fully test their products. Caveat emptor !

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