If you search internet for “2012 R2 Essentials” and “Hyper-V” you will see thousands of posts about this new added role, but hardly any describing how to really enable or install it. Even the TechNet article is somewhat vague when stipulating under Virtualize Your Environment that “depending on your system provider’s configuration, the Before you begin page provides an option to set up Windows Server Essentials either as a virtual instance or on physical hardware”.
Well, since this is a preview and no system provider can fix this for us, and furthermore I couldn’t find any reference about OEM SDK, or similar, that could configure Hyper-V for me in this manner, it is NOT possible to activate this option from the Before you begin page.
But nevertheless it IS well possible to install the Hyper-V role on 2012 R2 Essentials. For this purpose simply use the Server Manager and not the Essentials Dashboard:
Of course this is not as easy as a Dashboard Wizard, but, hey, previews are not for everyone :-p
Besides be aware that the Hyper-V is licensed only as a hardware hypervisor and you will eventually have to install the Essentials (for all other essential roles, pun intended) as a VM, which basically doubles the used space for OS files.
Also this means that you have to disable the essential roles on the Hypervisor partition (so that they don’t cross swords the VM), which is easily managed over the Server Manager as well. Thereby the Storage Services role is the only one that cannot be uninstalled, as shown below, but this is for a good reason, since you will most probably need storage for the VM images 😉 By the way for me the remove roles procedure needed two server restarts to take effect.
Lastly you can disable all features, either to minimize the attack surface and turn the Hypervisor to a Core installation. Be careful though – if you disable the PowerShell Feature as well, you will not only have problems fully administering your Hyper-V but also will get stuck if you want to go back to GUI-Windows.
If you however did disable every feature and now have only a command prompt then use the following sequence, as described by servervault:
dism.exe /online /enable-feature /featurename:MicrosoftWindowsPowerShellRoot
dism.exe /online /enable-feature /featurename:MicrosoftWindowsPowerShell /all
shutdown -r -t 0
Add-WindowsFeature Server-Gui-Shell, Server-Gui-Mgmt-Infra
shutdown -r -t 0
How do you switch between GUI and Core from three different perspectives, better have a look at this site.