The Volume Shadow Copy feature I wrote about last time is interesting enough (and quirky enough) that it seemed like a good idea to throw out a few more details. For starters, shadow copies are NTFS-only. Some admins report that the default NTFS cluster size of 4K is not as good as (say) 16K when using shadow copies, so you may want to research that a little further on your own. Another tip is that you can use shadow copies to revert an entire volume to a previous state, but this trick doesn’t work with the system volume.
Shadow copies can have “issues” with defrag programs, including Microsoft’s own. Apparently what can happen is that the defragger activity can be interpreted by the shadow copy service as file changes, triggering more shadow copy activity than necessary and in the worst case, even causing some shadow copies to vanish! If you’re using a third-party defragger, you should check with the manufacturer to see what steps you may need to take to safeguard your shadow copies. If you’re using Microsoft’s defragger, I suggest you do some testing with VSSADMIN to see what DEFRAG may be doing to your shadow copy inventory.
You might be interested to know that Microsoft is using shadow copies in Vista as well as in Server 2008 (and Server 2003). Not only is the “Previous Versions” client built into Vista (not Home versions though), Vista has the ability to create its own local shadow copies even if you’re not on a network. Vista also uses shadow copies for its System Restore feature.
Next time, I’ll talk about some useful shadow copy commands, so stay tuned.
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