Enabling Server and Desktop Virtualization

One of the most important aspects of any data center is providing the highest possible availability for systems and applications. Virtual data centers are no exception to the need for consolidation, high availability and most of all sophisticated management tools.

Hyper-V in Windows Server 2008 R2 includes the much-anticipated Live Migration feature, which allows you to move a virtual machine between two virtualization host servers without any interruption of service. The users connected to the virtual machine being moved might notice only a slight slowing in performance for a few moments. Otherwise, they will be unaware that the virtual machine was moved from one physical computer to another.

Even with all the efficiency gained from virtualization, virtual machines still need to be managed. The number of virtual machines tends to proliferate much faster than physical computers because machines typically do not require a hardware acquisition. Therefore, management of virtual data centers is even more imperative than ever before. Windows Server 2008 R2 includes the following improvements that will help you manage your virtual data center:

Hyper-V in Windows Server 2008 R2 now supports up to 64 logical processors in the host processor pool. This is a significant upgrade from previous versions and allows not only greater VM density per host, but also gives IT administrators more flexibility in assigning CPU resources to VMs. The new Hyper-V also adds performance enhancements that increase virtual machine performance and power consumption. Hyper-V now supports Second Level Address Translation (SLAT), which uses new features on today’s CPUs to improve VM performance while reducing processing load on the Windows Hypervisor and will also consume less power by virtue of the new Core Parking feature implemented into Windows Server 2008 R2.

Hyper-V R2 also includes a new Processor Compatibility feature. Processor compatibility allows you to move a virtual machine up and down multiple processor generations from the same vendor. When a VM is started with processor compatibility mode enabled, Hyper-V normalizes the processor feature set and only exposes guest visible processor features that are available on all Hyper-V enabled processors of the same processor architecture, i.e., AMD or Intel.  This allows the VM to be migrated to any hardware platform of the same processor architecture. Processor features are "hidden" by the hypervisor by intercepting a VM's CPUID instruction and clearing the returned bits corresponding to the hidden features.

The new Hyper-V leverages several new networking technologies contained in Windows Server 2008 R2 to improve overall VM networking performance. Two key examples are the new VM Chimney (also called TCP Offload) and the use of Jumbo Frames.

VM Chimney allows a VM to dump its network processing load onto the NIC of the host computer. This works the same as in a physical TCP Offload scenario, Hyper-V now simply extends this functionality into the virtual world. This benefits both CPU and overall network throughput performance, and it’s fully supported by Live Migration.

VM Chimney is disabled by default in Windows Server 2008 R2, primarily for short-term hardware compatibility reasons. But combined with compatible hardware, currently including vendors like Intel, VM Chimney significantly reduces the host server’s CPU burden when dealing with VM network traffic. This translates into better host system performance and a simultaneous boost to VM network throughput.

Like TCP Offloading, support for Jumbo Frames was also introduced with Windows Server 2008. Hyper-V in Windows Server 2008 R2 simply extends this capability to VMs. So just like in physical network scenarios, Jumbo Frames add the same basic performance enhancements to virtual networking. That includes up to 6 times larger payloads per packet, which improves not only overall throughput but also reduces CPU utilization for large file transfers.