Windows Server 2012 R2 Hyper-V features: Generation 2 virtual machines

What impact will the new Hyper-V Generation 2 virtual machines have on data storage?

One of the boldest new Windows Server 2012 R2 Hyper-V features is the ability to create Generation 2 virtual machines (VMs). Generation 2 VMs offer a number of exciting capabilities, many of which are directly related to storage.

In case you haven't heard about Generation 2 virtual machines, they are designed to be more efficient than first-generation VMs. They do not use emulated hardware, but instead make use of a fully exposed virtual bus. However, this change limits your operating system choices. In addition, Generation 2 VMs only support 64-bit editions of Windows Server 2012, Windows Server 2012 R2, Windows 8 or Windows 8.1.

Generation 2 VMs still make use of VHDX-based virtual hard disks, but the guest operating system now treats the VHDX file as a SCSI disk. Incidentally, Generation 2 VMs also support Preboot Execution Environment (PXE) booting.

From a storage management standpoint, the most significant benefit to using Generation 2 virtual machines is that they make it possible to dynamically resize storage on an as-needed basis. VHDX files can be expanded or compacted while the VM is running. This holds true even for boot VHDX files.

Other Hyper-V features available with Generation 2 virtual machines include the ability to clone or export a VM while it is running. A virtual machine can be cloned in its current state, or the cloning process can be based around a VM checkpoint. The checkpoint Hyper-V feature has replaced the Hyper-V snapshot feature.

Generation 2 VMs do not use emulated IDE controllers, but rather communicate with VHDX files using native SCSI commands. This leads to a significant increase in VM performance. Windows Server 2012 R2 is still in development, so no official performance benchmarks exist yet, but my own observations have been that Generation 2 VMs seem to boot approximately 30% faster than a Generation 1 VM running on comparable hardware. I have also seen a major performance improvement when it comes to OS installation. On my test servers, the OS installed on a Generation 2 VM in less than half the time that it took to install on a Generation 1 VM.

About the expert: 
Brien Posey is a Microsoft MVP with two decades of IT experience. Before becoming a freelance technical writer, Brien worked as a CIO for a national chain of hospitals and health care facilities. He has also served as a network administrator for some of the nation's largest insurance companies and for the Department of Defense at Fort Knox.