Microsoft has certainly not been considered the friendliest of the virtualization companies out there. They've added some sometimes significant hurdles to overcome, including additional license fees for virtual desktop environments and the company has some pretty strict (unreasonable?) policies in place when it comes to supporting their products in a virtualized environment.
However, there's another side to the Microsoft virtualization story.
Believe it or not, for some of their products, the company has among the most reasonable licensing policies I've seen from software vendors. In particular, Microsoft has some pretty good virtualization deals for Windows Server, SQL Server and the entire System Center product line. Of course, there is a point at which these deals begin to make financial sense and this line will be different for every organization, so some study is necessary.
- Windows Server. For organizations that buy a Windows Server Enterprise Edition license, they can deploy the physical Windows instance and up to four additional virtual Windows Server instances on that host server without having to pay additional license fees. For those that are willing to shell out the money for the Data Center edition of Windows Server (licensed on a per-processor basis), Microsoft allows an unlimited number of virtual Windows Server instances to run on the hardware. Better yet, you don't even have to be running Hyper-V to take advantage of this license allowance. As long as you buy Windows Server Enterprise or Data Center licenses and "soft apply" them to the host hardware – which could be running VMware ESX – you're covered. I should note that these licenses apply only to the server side of the licensing equation. You still need client access licenses (CALs) to access the server.
- SQL Server. Just like other Enterprise and Datacenter editions, SQL Server 2008 R2 Enterprise allows you to run up to four copies of SQL Server on a single host while the Datacenter edition allows you to run an unlimited number of SQL Server copies on a single physical server. It should be noted that I intentionally avoided using the word "instance" here and substituted copies in order to avoid confusion with regard to installing additional SQL Server instances on a single SQL Server. Regardless of which edition you choose, you can always run as many instances as you like, but the virtualization licensing allows you to install SQL Server into separate virtual machines.
- System Center. Microsoft makes available two software bundles that combine products from the System Center product line. Available in an enterprise bundle (Server Management Suite Enterprise [SMSE]) and a per-processor-based data center edition (Server Management Suite Datacenter [SMSD]), these bundles operate in a similar fashion as the Windows model. SMSE allows administrators to protect the physical host plus up to four virtual operating system environments with the single bundle while the SMSD bundle allows a company to protect an unlimited number of operating system environments on a single physical server. So, if you have four VMware ESX servers and each host sports two processors, in order to cover all of the operating system instances on all four hosts with the SMSD suite, you'd need to buy an eight processor license.
These are the products that currently enjoy the best virtualization licensing benefits from Microsoft. As you can probably tell, each option has the potential to save organizations a lot of money if there is adequate virtual machine density.