Using backup on Windows Hyper-V Server or Server Core

The Snapshot File Location for the VM is set to be the same volume in the host operating system as the VHD files for the VM.

I am not sure what happens if you have VHDs in several locations, as you might do if you wanted to optimize performance by having VHDs on different physical disks. [Update – apparently in Windows Server 2002 R2 the .AVHD snapshot files are always in the same location as their parent VHD, and this is on a per-VHD basis, so it should not be a problem in R2].

Third, there is a question mark about whether either method works for VMs running Active Directory:

Active Directory does not support any method that restores a snapshot of the operating system or the volume the operating system resides on. This kind of method causes an update sequence number (USN) rollback. When a USN rollback occurs, the replication partners of the incorrectly restored domain controller may have inconsistent objects in their Active Directory databases. In this situation, you cannot make these objects consistent.

I am also not clear whether archive bits are flipped in the child VM, if you use –vssfull along with the Child VM snapshot. If so, you should definitely not use –vssFull in the host if you are also backing up from the guest. I am trying to get clarification on these points.

These are more questions than I would like for something as critical as backup and restore of VMs. For peace of mind you should either shut them down first, which is unacceptable in most production environments, or else backup from the guest instead of, or in addition to, backing them up from the host. I’ll update this post when I get further information.

Data Protection Manager

Finally, note that in grown-up Microsoft environments you are meant to use Data Protection Manager (DPM) rather than fiddling around with wbadmin. There is even a white paper on how this integrates with Hyper-V. Ultimately though this is also based on VSS so some of the same issues may apply. However, if you are using the free Hyper-V Server 2008 R2, you are probably not in the market for DPM and its additional hardware, software and licensing requirements.

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Related posts:

  1. How to backup Small Business Server 2008 on Hyper-V
  2. No more infrastructure roles for Windows Nano Server, and why I still like Server Core
  3. Wrestling with Windows Server Core
  4. The virtual Small Business Server 2008 backup problem
  5. Installing .NET, PowerShell on Windows 2008 Server Core: it can be done

9 comments on this post.
  1. Duncan Smart:

    Interesting stuff. I’m investigating the same sort of stuff at the moment and am having good results using the VShadow.exe from the SDK ( in doing a volume snapshot and then exposing as a remote share which our existing (robocopy based) backup system pulls from. Something like this:

    vshadow -p -script=vshadowvars.cmd C:
    call vshadowvars.cmd
    vshadow -er=%SHADOW_ID_1%,MySnapshot

    …then we can backup \\server\MySnapshot,

    It’s interesting to watch the server using Hyper-V Manager as the “vshadow -p” comand runs and all the machines get automatically snapshotted. Ones without integration services (e.g. Linux) get briefly hibernated.

    (VShadow is probably already on your dev box if you have Visual Studio installed: C:\Program Files\Microsoft SDKs\Windows\v6.0A\Bin\x64\vsstools)

    I’ve shied away from using Window Server Backup because I have a hard-earned aversion to proprietary backup formats. But hearing that it uses VHD as its format means I might take a look now.

    Odd that you have to go through registry shenanigans to make Windows Server Backup work with Hyper-V, whereas it worked out of the box for vshadow.

    By the way, rhe install command is just “ocsetup WindowsServerBackup” (no “/install”)

  2. tim:


    Thanks for the info about vshadow, interesting.

    I’ve corrected the ocsetup command.


  3. Alan:

    I inherited a Hyper-V server with two VMs running on it. I’m looking for the best way to backup the VMs and thought this might be an option, but as USB is not recognized on the host, I don’t know how viable an option this is. Any recommendations that would not include buying a tape library or third-party software?

  4. tim:


    I don’t understand why USB is not recognized on the host? On the guest, yes. But you can back up from the host using the built-in backup, to an external USB drive.


  5. Zach:

    I don’t see a WindowsServerBackup key in the registry on Hyper-V Server. Is there another place to enable VSS for Hyper-V?

  6. Gary:

    Excellent Tim, thanks for alerting me to to this. In a small business environment, it not alway possible to have an extra server to test out the restore procedure, do you know if I could install VMWare on a XP 32bit machine, create guest VM then do a full restore of the wbadmin system backup? I think it would fail due to it being 32bit, wondered if you had any experience of this at all?


  7. tim:


    64-bit guest will only work on a 64-bit CPU.

    I have a spare machine running the free hyper-v server which I use for test restores.


  8. David Karlsson:

    I hope you can help me Tim. We have a core installed MS SRV 2008 R2 that is running one TS server and a file server, we are using a external HDD for backup.
    Now to my question: Is there any way to switch the external HDD wile the hyper-v server is running, to our second HDD with out having to reboot the hyper-v server?

    The two external HDD is identicle 1TB.
    Hyper-V server is a HP DL380 G7, with the HDD setup as this. 2 x 146GB system and 2 x 600GB for storage. This was before we started using 4 x 300GB in the raid 1+0.

    Tank you in advance!

    Best regard


  9. tim:


    Yes, you can switch them, what is the problem?