Disclaimer: I’m not a licensing expert, so check with your licensing experts to clarify licensing for your environment.

I’ve had a couple of questions today about licensing SQL Server in a virtual environment, so I thought I’d put up a little information on the topic.

Last year I published some information about our virtualization support for SQL Server, so if you haven’t already read it, it will fill out the story below.

Physical or virtual CPU?

If you have been in the market for a computer over the last few years you would have heard of things like HyperThreading (HT) and Multi-Core CPU’s. When running in a Virtual machine, SQL Server is licensed based on either the virtual CPU’s or the physical CPU’s.  We don’t differentiate between HT and cores, although cores do come into the equation in some cases.

Standard and Workgroup.

With SQL Server Standard, Web and Workgroup editions (whats the diff?) you purchase a license per virtual CPU – that is per virtual CPU configured in the virtual machine.

However, if you are looking to virtualize several machines onto a single physical server and licensing per processor, there is a calculation that can be used to work out the number of licenses, this will reduce the costs associated with the virtual environment.  If you are licensing on a Server/CAL basis (i.e. not Web Edition), the license is no different to licensing for physical hardware.

SQL Server Enterprise

One of the key benefits of SQL Server 2008 Enterprise is that virtualization is baked into the license agreement.  What this means is that if you license SQL 2008 Enterprise for your quad CPU server, you can run SQL 2008 on as many Virtual Machines on that quad CPU server as you can for no extra cost.