One of the biggest limitation of Virtual Server 2005 was the impossibility to backup the running virtual machines with NTBackup.
When Microsoft moved to Windows Server 2008 and Hyper-V this limitation was finally removed, but the capability is not exactly out of the box.
To achieve the goal customers must manually create some new keys in the Windows Registry so that the Hyper-V Volume Shadow Service (VSS) writer can interact with the new Windows Server Backup (WSB).
The configuration also has some serious limitations:
- WSB only supports volume based backups: if the VM configuration file and the actual virtual hard drive (.VHD) are stored in different volumes, all volumes must be selected.
Conversely, when performing a recovery from backup, the entire volume or volumes must be restored.
- Live backup is not supported for those VMs that have dynamic disks. In such case only offline backups can be performed.
- If the VM has more than one snapshot the restore will fail (there’s a workaround for this)
- Live backup is unavailable for those guest OSes that don’t support VSS, like Windows 2000 or XP, as well as those guest OSes that don’t have the Hyper-V Integration Services installed.
In such cases WSB will put the VM in a saved state, backup the snapshot, and finally restore the VM.
Of course Microsoft has all the interest to keep these limitations so that most demanding customers will be forced to look at the new Data Protection Manager 2007 SP1.