In this article, we’ll look on licensing features of the Windows Server 2019, 2016 and 2012 R2 operating systems from the point of view of new Microsoft licensing model. Also, we’ll tell about the rules and licensing procedures when using Windows Server as a guest OS in a virtual machines, including the HA clusters with the ability to migrate virtual machines between hypervisors (VMWare VMotion, Hyper-V Live Migration, etc).

Starting from Windows Server 2012, Microsoft has changed and simplified the licensing model of its server platform. Now it meets the modern tendencies to extensive use of virtualization technologies.

Windows Server Editions

In most cases, when considering the Windows Server licensing model, it is advisable to consider the Standard and Datacenter?Windows Server editions.

The features of the Standard and Datacenter editions of Windows Server 2012 R2 is almost identical except for the license rights to run virtual machines. It means that you choose the edition depending only on the number of virtual machines on the physical host instead the availability of the required features.

• Windows Server 2012 R2 Standard – the license allows to run only up to two virtual machines;
• In Windows Server 2012 R2 Datacenter – you can run an unlimited number of virtual machines on a single physical host (recall that such virtual machines can be easily activated using the AVMA – Automatic Virtual Machine Activation).

In fact, when choosing Windows Server 2012 R2 Edition you need to decide whether you will use virtualization or not.

The Windows Server 2016/2019 Standard license also allows you to run up to two VMs with Windows Server on the same physical host.

Windows Server 2016 and 2019 Datacenter support a number of new technologies that are useful in a virtualization and the Azure cloud environment. For example, the Windows Server 2016 Datacenter supports:

• Storage Spaces Direct
• Storage Replica
• Shielded Virtual Machines
• Host Guardian Service
• Network Fabric
• Microsoft Azure Stack

Per-Socket Licensing in Windows Server 2012 R2

One license of Windows Server 2012 R2 allows you to run the OS on one single- or dual-processor server. I.e. one license covers up to two processors (sockets) located in one physical server (cores are not processors!). You cannot split one license for two single-processor servers (in this case you will have to purchase two Windows Server licenses). If a physical server has more than two processors, you will have to buy one license for each pair of processors. For example, for a 4-processor server you will need 2 Windows Server 2012 R2 licenses.

Windows Server 2016 and 2019: Per-Core Licensing

Microsoft switched from the licensing model of physical processors to the core licensing model (Core-based) in Windows Server 2016 and Windows Server 2019. This is due to the tendency of CPU and server manufacturers to increase not the number of processors, but the number of cores on a single socket (Microsoft doesn’t want to lose profits when customers start to widely use multi-core servers). Note the main points of Windows Server 2016 and 2019 licensing model:

• 1 license of Windows Server 2016 allows you to license 2 physical cores on a single server (i.e., Microsoft ships two core licenses);
• The cost of one 2-x core license is 8 times reduced comparing to a one single processor license for Windows Server 2012 R. However, you need to buy at least 8 such licenses (for 16 cores) – this is the minimum package for 1 physical host. Thus, the licensing cost for one physical 2-processor server with up to 8 cores per socket has not changed. The following licensing rule is true: 1 * Windows Server 2012 R2 (2 CPU) = 8 * Windows Server 2019 (2 Core);
• Now also 16-core WinSvr licenses available, allowing you to quickly license 1 standard physical host (for example, WinSvrSTDCore 2019 SNGL OLP 16Lic NL CoreLic);
• All enabled cores on a physical server must be licensed.

Understanding Windows Server Virtual Machine Licensing

If you plan to use your physical server as a hypervisor on which several VMs with the Windows Server are running, you need to choose the OS edition depending on the number of VMs that will be running on your server.

For example, you have a dual processor server with total 16 cores. If you purchased 8 licenses of Windows Server 2019 Standard and licensed all the physical server cores, you are allowed to run up to 2 VMs with a Windows Server on a licensed physical host. The Datacenter license allows you to run an unlimited number of virtual OSs on a licensed host.

What if you need to run more than two virtual machines on a server with a Standard license? You will have to buy the required number of licenses based on the following consideration: one Standard license allows you to run 2 virtual machines.

For example, you want to license a dual-processor (8 cores per CPU) server with four virtual machines. According to the Windows Server 2016 Standard licensing model, you need to buy 16 dual-core Window Server Standard licenses (2 sets of licenses closing all physical cores) or 8 dual-core Datacenter licenses (you can upgrade Windows Server 2016 edition without reinstalling).

Note that the licensing procedure is as follows: first the physical cores are covered, and then the virtual machine instances.

According to the current Microsoft prices, it is worth to buy the Windows Server Datacenter edition if you are going to run 14 or more virtual machines on one physical host. If the number of VMs is less, it’s better to get several Standard licenses to suit your cores and VMs demands.

If you use virtualization on your physical server with Windows Server 2019, you can use the host OS only to maintain and manage the Hyper-V role and virtual machines. You cannot install Windows Server 2019 on a physical server, run two VMs on it and get three full-fledged Windows server instances for your tasks. In Microsoft terminology, the physical OS instance is called POSE (physical operating system environment), and virtual – VOSE (virtual operating system environment).

Windows Server Licensing and VMs Migration between Physical Hosts

Further we’ll consider licensing peculiarities if the Windows Server virtual machine can move between physical servers in a virtualization farm (using VMotion, Live Migration, etc.).

Software Assurance (SA) provides the right to transfer the product license between physical hosts for most Microsoft server products. But Windows Server is an exception to this rule. According to the licensing agreement, the license can be migrated between the hosts once in 90 days.

How to license a virtualization farm, in which VMs can move between hypervisors (host OSs)? In this scenario, you will have to buy that number of licenses for each physical server covering the maximum number of virtual machines that can be run on it at any time (including the high availability scenarios when all virtual machines of the farm are moved to the one of the hosts). I.e., the virtual machine licenses are linked to a physical host and do not move between the hosts together with the VMs.

For example, for two separate single processor physical servers with two virtual machines on each of them, we’ll need 2×8 Windows Server Standard licenses.

However, if the virtual machines can move between these servers, we’ll need another set of 2×8 licenses (providing that 4 VMs can be run simultaneously on each server).

In the case of the Datacenter edition, one set of licenses will be sufficient for each physical host, covering all cores (in the minimum configuration, 8 Datacenter dual-core licenses). Since this license allows you to run an unlimited number of VMs.