Disappearing VM's ?

I have Ubuntu 7.01 running as host on an ext3 partition on one drive and two ntfs partitions on two other drives. The VMs are on one of the ntfs partitions. In my VM folder I had (notice the past tense) 4 vm's -- copies taken at stages of development and I was working with vm 4.

In my crontab I was backing up the vm 4 each night, bzipping it to the other drive ... thank goodness. It had run several days like that without being rebooted -- either linux or the xp vm.

Then one day I decided to reboot the vm for something and got an error on exit that the 'hard drive' file for vm 4 did not exist. I then checked the Virtual Machines folder and it was empty -- none of the vm files, i.e. the "hard drives" were there. I checked my backups and the backup from the prior night had not worked ... because the file was not present.

So ... somehow these files were deleted ... parallels was still operating presumably because the file itself was in 'trash' or 'recycle bin' somewhere but then was deleted upon close. I was able to recover to the version from two days earlier ... so the bzip worked -- except that on 'power on' windows had to do a disk check on the file likely because it was changing while it was being backed up (20 gb takes a while to bzip) and do some cleanup, which could have been the pagefile or anything in xp.

So -- I heartily recommend a nightly backup -- 20gb was being compressed to 6.5 gb. I'm also using logrotate to rotate the backups.

But -- I still don't know what happened to the files. I'm sure that if someone had gotten through my firewall something else would have been deleted other than these 4 files.

Has anyone had any experience with disappearing 'hard drive' files ??

Thanks.