Hi,
here's the link to its beta for you to try out:
http://www.paragon-software.com/home/snapshot-mac/
Basically it creates a snapshot of the file system at block level which can be saved to an image or directly mounted, thus allowing for backups of open files, in use databases, etc. It's similar to VSS on Windows. I'm currently testing it and recently asked others for their experience, but noone replied so far:
http://discussions.apple.com/thread.jspa?threadID=2062942&tstart=0
The Mac's current filesystem (HFS+) does not support snapshots on its own. I did a bit of research and the Paragon Snapshot beta seems to be the only software for this. If Apple one day includes full ZFS support it would help, since ZFS has this ability. But I believe it will be a while. I'm beta-testing 10.6 Server/Client and even though I was asked if I was interested in testing ZFS there's currently no full support built-in...
My tests with the PS beta worked fine so far, but I didn't test on a live production Xserve...
Hope this helps and if you decide to try it out, feel free to leave a reply on my thread. 🙂
Björn