Windows Insider

Hyper-V Licensing: Make Sure You're Compliant

Read the fine print to understand Hyper-V licensing, which comes with some caveats.

• By Greg Shields
• 02/14/2011

As I travel the country presenting and consulting on virtualization topics, I'm constantly bombarded with questions about Hyper-V licensing. With a Hyper-V host being the same Windows Server as the guests it runs, you can imagine the difficulty in figuring out exactly what you need to license to ensure compliance.

That's why, not long ago, I dug deep into the Hyper-V licensing language to get the real scoop. While I'm no contract lawyer, I found myself surprised by a few of the licensing terms even I wasn't aware of. Read on for the short list of those terms that could bite you in your next licensing audit.

First up is the question about Client Access Licenses (CALs) for Hyper-V hosts and guests. You already know that CALs are required for every client that connects to a Windows server and makes use of its services. What I didn't know, however, is that Windows Server 2008 R2 CALs are in fact not required for Hyper-V host computers -- the computers that run Hyper-V virtual machines (VMs). Any VMs running on top of that host obviously have a CAL requirement, but if your Hyper-V host is simply that and nothing more, it's safe without them.

My second discovery deals less with a licensing gotcha and more with a poor naming choice. You know that Hyper-V is a role that installs to an existing Windows Server 2008 or Windows Server 2008 R2 instance. But you might not be aware of the free -- and horribly named -- Microsoft Hyper-V Server product. This product is free because it arrives as a severely limited version of Windows Server Core Edition that's been locked down to only run the Hyper-V role and associated services such as Windows Failover Clustering. It's horribly named because Hyper-V and Hyper-V Server sound like the same thing. They're not. Hyper-V Server is free, so you can use it wherever you like. That said, always remember that you'll need appropriate licensing for every VM you run on top.

The Fine Print
A third realization shocked me when researching the much-ballyhooed Microsoft "four-for-one" deal.

Microsoft licensing language allows for four additional virtual OS instances to run atop every physical instance of Windows Server 2008 or Windows Server 2008 R2 Enterprise Edition. This buy-one-get-four-free language has been around since the release of Windows Server 2008, and is a great bonus to shops that have invested in Enterprise Edition's step-up pricing.

However, there's a not-well-known restriction on that four-for-one that many shops have inadvertently ignored. Quoting from the Microsoft Windows Server 2008 R2 Licensing FAQ page, you'll be surprised to know that:

"The rights to run the four instances are assigned to the licensed server, and all the instances can run only on the licensed server ... You may not move your rights to run [for example] an additional two instances to another server. However, if you have another server that's licensed for Windows Server 2008 R2 Enterprise or Datacenter, you may move the two workloads to that server and run them on that server provided that by running the additional instances you do not exceed the licensed capacity of the new server (one with Windows Server Standard, four with Windows Server 2008 R2 Enterprise, and unlimited with Windows Server 2008 R2 Datacenter)."

Wow. To me, this means once you've exhausted your first four instances, every additional VM requires additional licensing. That same FAQ page continues with the statement: "If you want to run a fifth instance in a virtual operating system environment, you must acquire and assign an additional license to that server."

The moral of this story is "don't assume." While Microsoft's freebie deals seem like an immediate win, they come with some dangerous strings attached that could cause you problems down the road.