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If you are considering deploying Microsoft's Hyper-V, then you probably know that Microsoft provides two different flavors of Hyper-V. There are two approaches to Hyper-V installation that system admins have the option to choose from. Hyper-V can be installed as a server role in Windows Server or you can opt to use the standalone Hyper-V Server. But which is better, and which should you use?
When deciding between Hyper-V Server and Windows Server 2012 R2 with Hyper-V, there are two main criteria that you must consider: licensing needs and the capabilities you need to utilize. Let's talk about the licensing requirements first.
As you may have heard, Hyper-V Server 2012 R2 is free. You can download it, install it, and use it forever without ever having to pay a licensing fee to Microsoft. Best of all, Hyper-V Server offers the same capabilities as Windows Server 2012 R2 Hyper-V. Better still, Hyper-V Server is not burdened with a true host operating system. It is a bare metal hypervisor, and therefore lighter weight than its Windows Server counterpart. This translates directly to a smaller potential attack surface, and possibly to better overall performance and lower resource consumption.
Of course this raises the question of why anyone would pay for a Windows Server 2012 R2 license for their Hyper-V host servers when they can get Hyper-V for free simply by downloading Hyper-V Server. From a licensing standpoint, there is one distinct advantage to using Windows Server 2012 R2 Hyper-V. When you purchase Windows Server 2012 R2, the license that you purchase grants you permission to install Windows Server 2012 R2 onto your virtual machines. Windows Server 2012 R2 Standard Edition isn't really suitable for this purpose because it includes such a small number of virtual machine licenses, but the Windows Server 2012 R2 Datacenter Edition license allows you to install Windows Server 2012 R2 onto an unlimited number of virtual machines, so long as all of those virtual machines are running on the licensed host. Conversely, if you opt to use Hyper-V Server then you will have to pay for operating system licenses for all of your virtual machines.
At first, the idea of having to individually license the operating systems for numerous virtual machines sounds cost prohibitive. However, in some situations it is possible to avoid spending any money. Consider a situation in which you want to perform a physical to virtual migration of some of the servers in your data center. Presumably, the operating systems on those servers have already been licensed. If that's the case, then those licenses will usually transfer to the virtual environment, which means that you don't have to worry about purchasing operating system licenses for the virtual machines. Similarly, you may be able to avoid purchasing operating system licenses for future virtual machines by using an open source operating system. Of course, if you want to install Windows on new virtual machines, then you will have to appropriately license the Windows operating system.
Other server roles and capabilities
The other criterion for evaluating which hypervisor is best suited to your organization is the capabilities that you need to utilize. As previously mentioned, the free Hyper-V Server includes exactly the same capabilities as Windows Server 2012 R2 Hyper-V. Even so, it is worth mentioning that in the case of Windows Server 2012 R2, Hyper-V is one of many different server roles that are available. If Hyper-V is the only role that you need (and there aren't any licensing issues that have to be considered) then you can probably go with Hyper-V Server. If, on the other hand, you need to use some of the Windows Server features or capabilities that are not directly related to Hyper-V, then you are going to be better off deploying a full Windows Server operating system.
Hyper-V Server is free, but lacks a true GUI or parent OS. The preferred method of managing Hyper-V Server involves using Windows PowerShell, but it is possible to remotely manage Hyper-V Server using the Windows Server Manager and related tools such as Hyper-V Manager. In case you're wondering, it is possible to join a server that is running the free version of Hyper-V to an Active Directory domain. You can even include the server in a failover cluster. As such, you are not giving up any features or capabilities by going with the free version of Hyper-V as opposed to installing Hyper-V as a Windows Server role. You simply need to consider the licensing implications and whether or not you will need to use any of the other Windows Server roles or features.
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