Tag Archives: hyper-v

microsoft, virtualization

Bare-metal recovery of a Hyper-V virtual machine

Over the weekend I ran some test restores of Microsoft Hyper-V virtual machines. You can restore a Hyper-V host, complete with its VMs, using the same technique as with any Windows server; but my main focus was on a different scenario. Let’s say you have a Server 2008 VM that has been backed up from the guest using Windows Server Backup. In my case, the backup had been made to a VHD mounted for that purpose. Now the server has been stolen and all you have is your backup. How do you restore the VM?

In principle you can do a bare-metal restore in the same way as with a physical machine. Configure the VM as closely as possible to how it was before, attach the backup, boot the VM from the Server 2008 install media, and perform a system recovery.

Unfortunately this doesn’t work if your VM uses VHDs attached to the virtual SCSI controller. The reason is that the recovery console cannot see the SCSI-attached drives. This is possibly related to the Hyper-V limitation that you cannot boot from a virtual SCSI drive.

The workaround I found was first to attach the backup VHD to the virtual IDE controller (not SCSI), so the recovery console can see it. Then to do a system recovery of the IDE drives, which will include the C drive. Then to shutdown the VM (before the restart), mount both the backup and the SCSI-attached VHDs on the host using diskpart, and use wbadmin to restore each individual volume. Finally, detach the VHDs and restart the VM.

It worked. One issue I noticed though is that the network adapter in the restored VM was considered different to the one in the original VM, even though I applied the same MAC address. Not a great inconvenience, but it meant fixing networking as the old settings were attached to the NIC that was now missing.

I’ve appended the details to my post on How to backup Small Business Server 2008 on Hyper-V.

virtualization

USB devices and Hyper-V – remote client yes, host no

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At TechEd in New Orleans, Microsoft has announced that the version of Hyper-V in Windows Server 2008 R2 Service Pack 1 – a typical Microsoft mouthful – will include support for generic USB devices. That is, you can remote into a Hyper-V VM, plug in your USB camera, scanner or bar-code reader, and it will be re-directed to the remote desktop.

It’s a welcome feature, and removes one of the annoyances of working on a remote desktop. However, there is another scenario that Microsoft has not addressed, which is support for USB devices on the Hyper-V host. For example, USB drives are often used for backup, but if you plug a USB drive into a Hyper-V host, it is not easy to use it for backup from within a Hyper-V guest. Well, there are ways, but you are not going to like any of them – mount the drive in the host, mark it as offline, attach it to the guest using pass-through, and so on.

So will Hyper-V ever support USB devices in the host as well as on remote clients? I asked about this, and was told that it is not a priority, because although the topic comes up regularly, it is “not in the top ten feature requests”.

That’s a shame. Even if Microsoft supported only USB storage devices, it would help significantly with tasks like backing up Small Business Server when run on a virtual machine.