ESU licenses correspond to the number of underlying core licenses of your server or operating system. You can license Windows Server and SQL Server based on either physical cores (pCores) or virtual cores (vCores). With ESUs sold through Commercial Licensing, the licenses must align with how you've licensed the underlying Windows Server or SQL Server.
Physical Core Basis: If you choose this option for your underlying software, you'll need an ESU license for each physical core on the server. All validly licensed guest VMs running on the host are covered without the need for additional licenses. (Note that Windows Server and SQL Server software editions have different allowed virtualization entitlements for the number of guests allowed.) Windows Server has an 8-core minimum per processor and 16-core minimum per server for pCore licensing. SQL Server has a 4-core per processor minimum.
Virtual Core Basis: If you opt for this option for your underlying software, you'll require an ESU license for each virtual core assigned to the VM. Windows Server has an 8-core minimum per VM for vCore licensing. SQL Server has a 4-core per VM minimum.
In summary, when licensing with Commercial Licensing ESUs (SKUs), the number of ESU core licenses must align with how you've licensed the underlying Windows Server or SQL Server. Also, with the Commercial Licensing ESUs, you must ensure that the ESU edition matches the edition of your underlying software. For instance, if you have Windows Server Datacenter on your VM, you should acquire ESU Datacenter edition if you want to license at the vCore level.
Note
The majority of WS 2012 licenses were sold on a per Processor or per Core basis (not on a per VM basis). For purposes of ESU core calculation, assume each 2 Processor license (the minimum per server) is equivalent to 16 pCores.
Examples:
Physical Core Scenario: A customer with a 16-core server licensed with Windows Server Datacenter on a pCore basis will need to acquire 16 ESU Datacenter licenses. This covers the entire server regardless of the number of guest VMs running on it.
Virtual Core Scenario: A customer with three 8-core VMs licensed with Windows Server Standard on a vCore basis will need 24 ESU licenses of the Standard edition to cover all VMs. When adding an additional VM, additional ESU licenses must be acquired accordingly. For VMs larger than eight vCores, i.e exceeding the minimum, add up all the vCores to get the correct price.Knowing your underlying license status for a given server enables you to accurately determine the number of Extended Security Update licenses you'll need.