Licensing SQL Server is often confusing, and the rules have changed. Here is a snapshot of how to license in high and low density virtual environments:
For smaller environments or low density environments the option to license individual virtual machines can be considered. When licensing by core, each virtual core or virtual thread in a hyper-threading architecture must be allocated with a minimum of four cores per virtual machine. This can be a very attractive configuration when the physical server is very dense and only a small percentage of the cores are supporting SQL Server.
–For the Standard Edition and the Business Intelligence (“BI”) Edition which can be licensed in “Server+CAL” metric, one server license is required for each VM.
For the larger or high density environments, the arithmetic works against the individual virtual machine licensing scheme, so licensing the physical server is more effective. In the “Server+CAL” metric, the license entitlement for the BI and Standard editions is one instance – either the physical instance or the virtual instance. For Enterprise Edition, which is no longer available except as an extension of Software Assurance, a single license in the “Server+CAL” metric entitles you to up to four instances.
You cannot have a conversation about Microsoft licensing without mentioning Software Assurance, and in this case Software Assurance also plays a key role in maximizing your virtual environment in the “Per Core” license model. Unlimited virtual machines supporting SQL Server are an entitlement under two conditions:
(1) When all the physical cores are licensed; and
(2) When all of these licenses are covered by Software Assurance – in other words, unlimited virtualization in SQL Server has now become a Software Assurance benefit.
That same configuration is also necessary when virtual machines supporting SQL Server might be moved from one node to another within a multi-node cluster. Software Assurance will not only provide you with unlimited virtual instances but also license mobility. Our recommendation is to plan that environment, look ahead very carefully, very deliberately, and then do the math and find out which way represents the most affordable method for you.