There’s a really compelling back-up and restore scenario for virtual machines: if something goes wrong, you can restore the saved machine to any hypervisor-compatible hardware. Since today’s hypervisors, including Hyper-V, tend to run on a broad class of hardware, and since most “bare metal” back-up technologies are sensitive to hardware changes, this feature alone can save you from having to rebuild a critical server from scratch.

The Active Directory domain controller server role is an example of where that scenario would be highly valuable, especially in the case of the Small Business Server SKU. Unfortunately, while Microsoft does support running Domain Controllers (including SBS) on Hyper-V, taking snapshots (or saving a copy for later restoration) technically isn’t supported (see also here). This is, again, unfortunate.

As an aside, I just found a good link that answers some of my questions about how the new Windows Server 2008 built-in back-up tool, wbadmin, supports Hyper-V. Turns out there’s a feature-specific VSS writer that must be explicitly enabled.

But I don’t understand how restoring a DC guest image with wbadmin is any more or less risky than restoring one from a HV snapshot. In fact, based on my understanding of the underlying technologies, the latter still sounds less risky (for example, you’re separating any issues with the restore failing for the host volume). And yet the former is supported and the latter isn’t?

This also raises questions for folks who are using tools such as Acronis or Symantec with HV hosts. Anybody know what special sauce is in wbadmin, or whether this is all just FUD?

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