How to calculate proper Windows Server 2012 virtualization licensing

Licensing virtual servers can get confusing and expensive. Brien Posey shares the ins and outs of server licensing with a Windows Server 2012 example.

Since server virtualization can complicate licensing, make sure that you understand the licensing requirements before you begin deploying virtual servers. It could even save you money.

Thanks to server virtualization, you can move a running virtual server from one physical server host to another without taking it offline. Server virtualization makes it so easy to deploy new servers and shuffle them around, however, that you may be violating your server licenses.

In the virtual data center, hypervisors, operating systems and applications all require licensing. Note: this discussion focuses solely on virtual servers, because virtual desktops bring in a completely different set of rules regarding licensing.

Although there are exceptions -- more on those in a moment -- you must use these different types of licenses in your virtual data center:

• Hypervisor licenses

• Virtual server operating system licenses

• Virtual server client access licenses

• Application licenses

• Application client access licenses

Windows Server 2012 virtualization licensing example

Virtual servers are licensed similarly to physical servers. For example, a physical server running Windows Server 2012 and Exchange Server 2013 would require a Windows Server 2012 server license and an appropriate number of client access licenses, as well as an Exchange Server license and an appropriate number of Exchange client access licenses. Additional licenses may be required for utility software, such as antivirus applications or backup agents.

If this same server was virtualized, then the Windows and Exchange licensing requirements would stay the same, with the addition of a hypervisor license. So far, virtualizing Windows Server 2012 is adding licenses and licensing costs for the server.

Virtual server environments can require a considerable number of licenses, which gets expensive. Many software vendors now take virtualization into account with regard to licensing. Savvy organizations can get some significant cost savings out of virtualization-aware licensing.

Probably the best example of virtualization-aware licenses is Microsoft's policy for Windows Server 2012. If your host server runs Windows Server 2012 and Hyper-V (and no other applications), you are entitled to a specific number of virtual instances of Windows Server 2012, in accordance with your edition. (A similar policy also exists for Windows Server 2008 R2.) If you purchase a Windows Server 2012 Datacenter Edition license, you can legally run an unlimited number of virtual machines (VMs) on that host server. Incidentally, the same basic licensing policy also applies if the Windows Server 2012 VMs are running on top of VMware ESX/ESXi.

Beware license violations due to virtualization

One oft-overlooked aspect of virtual server licensing is the effect that VM migration technologies, such as failover clustering and Microsoft live migration or VMware vMotion, have on licensing requirements.

Windows Server licenses are bound to the hardware. For example, if you purchase a Windows Server 2012 Datacenter Edition license, that license entitles you to run an unlimited number of Windows Server 2012 virtual instances on one physical server.

What happens if you move a virtual server from one physical host to another? That move could result in a license violation, unless the second physical host already contains a license that can accommodate the newly migrated VM. In this example, the new physical host requires a Datacenter Edition license or a Standard Edition license with VM instances still available.

Microsoft offers a few exceptions to this licensing policy. You can actually reassign a Windows Server 2012 license to a different physical host, so long as the license has not been reassigned within the last 90 days. The 90-day limit only applies to physical hosts and does not affect VMs moving between properly licenses hosts.

The 90-day restriction helps prevent short-term license assignments, and the company will let you reassign licenses on an as-needed basis in the following situations:

• Reallocating processors from one licensed hardware partition to another

• Creating two or more licensed partitions from a single licensed hardware partition

• Creating a single partition from two or more licensed hardware partitions (as long as the total number of licensed processors remains constant)

• Moving the license to another server as a result of permanent hardware failure.

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