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January 2009 Updates to Microsoft Virtualization Licensing Briefs

Microsoft has updated it’s licensing policies regarding virtual machines hosted on all versions of Hyper-V again. Available for download via the Licensing: Virtual Environments and Technologies web page, 2 key Microsoft virtualization policy documents now have Jan ’09 revisions. A description of these documents is provided in the page’s Overview section:

Licensing Microsoft Server Products in Virtual Environments (Word file, 2.25 MB) is an overview of Microsoft licensing models for the server operating system and server applications under virtual environments. Licensing Microsoft Windows Server 2008 to Run with Virtualization Technologies (Word file, 1.39 MB) describes how Windows Server 2008 and other Microsoft server products are licensed when they are used with other virtualization technologies.

Here are some quick notes on the changes from these documents that caught my attention.

The usage rights around storing multiple instances of VMs is a whole lot clearer.

This is helpful to understand when implementing VM back ups or DR fail over of Windows guests

Storing Instances

If a server is licensed, then stored or non-running instances of Windows Server and other Microsoft servers do not require separate licenses. The use rights permit you to store any number of instances under each license. You can also store instances on a large storage area network (SAN) or store instances on your servers without needing additional licenses for each instance.


As described earlier, you may store any number of non-running instances of server software on a server or in a library. You may run these instances only on any server that is licensed. If you need to run more instances on the server than the license permits, you may assign additional licenses to the same server. By assigning several licenses to a server, you may run as many instances of the server software simultaneously as the assigned licenses combined allow.

Understand the concept of Licensing for Peak Capacity.

This directly impacts the design and planning for potential live migration or VMotion of guests. VMware once described this to me as the need to plan for a “high tide” of VMs on each host and make sure you assign enough Windows licenses for that “high water mark” of guests. More explanation from the brief:

For example, if you have one Windows Server 2008 Standard license assigned to a server, you may run one instance of Windows Server 2008 Standard in the physical OSE and one instance of Windows Server 2008 Standard in a virtual OSE on the server at the same time. You may not run a second instance of the software in another virtual OSE on the server. If you need to periodically run a second instance in a virtual OSE, then you must assign a second license to the server.

Windows Server Licensing on top of VMware’s ESX.

If you already understand the allowed number of VMs per version of Windows (Standard allows 1, Enterprise allows 4, and Datacenter allows unlimited) this is not really new, but it is worth reviewing again. The key is that even though you do not install Windows Server on the bare metal, you still have to have Microsoft licensing for the hardware to host Windows guests. I’ve posted before about how using he Datacenter edition may make the most sense for this scenario. The briefs have specific language for ESX hosts:

If a server is running ESX as the virtualization technology, then Windows Server is not deployed as a host operating system in the physical OSE. However, a license is required for every instance running in a virtual OSE.

If you have assigned a single license for Windows Server 2008 Standard to a server running ESX, then you may run one instance of Windows Server 2008 Standard at a time. The right to run an instance of Windows Server 2008 in the physical OSE cannot be used in this case since ESX runs on the physical OSE (and as a result, Windows Server 2008 cannot be deployed as the operating system on the physical OSE.)

If you have assigned a single license of Windows Server 2008 Enterprise to the server running ESX, then you may run up to four instances at a time of Windows Server 2008 Enterprise. You may not run a fifth instance under the same  license since that right requires that the fifth instance be running hardware virtualization software and software managing and servicing the OSEs on the server.

Licensing for VMware’s VMotion and Live Migration seems to be more understanding, but relies on the proper planning for the peak capacity concept discussed earlier.

For Windows Server software, except in a few cases (see “Assignment of Licenses” above), licenses may only be reassigned to new hardware after 90 days. This, however, does not restrict the dynamic movement of virtual OSEs between licensed servers. As long as the servers are licensed and do not simultaneously run more instances than the number for which they are licensed, you are free to use VMotion and System Center Virtual Machine Manager to move virtualized instances between licensed servers at will.

Microsoft adjusted their CAL requirements when hosting Windows guests on hypervisors other than Hyper-V.

For more about the CAL policy changes check out some other bloggers’ posts:

Chris Wolf has covered the MS licensing changes and shortcomings extensively over the past year, and he has another post worth reading:  Another Microsoft Licensing Policy Update: What’s Good? What’s Left?

VMware’s Mike Dipetrillo posted Microsoft Licensing Update – Customers Win.

Finally, a good post on the Microsoft SMB Community Blog explains the CAL policy changes in detail.

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