How to back up a vhd automatically? Is there any tool which I can set up?
If you have a usb storage you can just windows server backup or windows backup and restore if you are on windows 7 ;
Windows Server Backup, backsup in vhd format too - so you can either restore the whole box or you can mount your backup drive, take ownership of the backup folder, browse to the directory and attach the vhd as a readonly option in Windows 7 and Windows 2008 R2, then browse the contents of your vhd file, so if you had some vms running on this server, you can extract those vhd's too.
there are other tools available which may allow you to mount vhd's in xp / vista too but windows 7 have it native.
You can schedule a windows server backup to backup whole server and that should do the trick,.
Have a look at some of the articles on HyperVoria that deal with backups you may get some pointers on what to implement for your infrastructure.
NOTE: I use WHS to backup all my HyperV VM's, then I just have to backup the VHD's for the WHS image itself. Recovery is done by the WHS recovery media (yes, I have tested this)
The beauty of this tool, is that the output file is a VHD file. This means that you can mount it on another server and work with the files. Since this VHD is a backup "copy" it is not locked in the way that a Hyper-V guest's VHD would be, so you can simply use robocopy to move it to your backup server.
I presume you're trying to backup Hyper-V VHDs, which would be locked so you cant simply copy it. The server backup tool will use VSS to take a snapshot so when you mount the main backup VHD file, all the other files inside will not be locked.