How do i take incremental backup of MS Virtual Machine vhd file that hasnt been updated?

I have a few servers running MS Virtual Machine. They use vhd files as disks and use veritas net backup to backup the whole host server. It runs a full backup once a week and incremental every other day. The thing is that the vhd files doesnt get updated untill you reboot the VM or shut it down. So Veritas Netbackup wont know its been updated. Is there any nice way to handle this?
An idea i have but dont really like is to "touch" the files once a day to change the modified stamp on them.

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not really..
backups of the vhd is not worth it until the vhd is updated.
in general a incremental of the vhd is not going to work right to start with.
i would suggest that backing up the vhd is a good way to image the system now and then, but to get the data
do a backup of the logical drive of the system just as if it were a regualar server.
gobbalobbaAuthor Commented:
Well the problem is that i dont have access to the guests. Thats why I want to take backup on the disk files. Hmm but if VM doesnt write to the files untill its saved or shut down it wont matter if i "touch" them right? Cause the data in them will still be the same since it started?
Maybe i have to put all machines in saved state and power on everyday to save the image and get a backup everyday.
that would the the only other option i see if you dont have access to the guest os.
gobbalobbaAuthor Commented:
I solved it with shadow copy.

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