Virtualization shoot-out: Microsoft Windows Server 2008 R2 Hyper-V

Microsoft's server virtualization platform pairs good performance with extensive management, at the cost of significant added complexity

Senior Contributing Editor, InfoWorld |

Late to the virtualization game, Microsoft has been running several lengths behind the competition in this space for years. However, the new features and strong performance present in Windows Server 2008 R2 SP1 show that the company hasn't been twiddling its thumbs. It's clearly been working hard at bringing a compelling and competitive virtualization solution to the market.

There's plenty to like in Hyper-V these days, not the least of which is the price comparison to the other major players. But whereas that lower price used to mean significantly diminished features and performance, that gap has closed. Hyper-V now offers the big features, including live VM migrations, load balancing, and high availability, as well as a more fluid management interface in Microsoft System Center Virtual Machine Manager 2008 R2 (VMM).

One very notable addition to Hyper-V in Windows Server 2008 R2 SP1 is dynamic memory. By specifying a minimum and maximum RAM allotment per virtual machine, as well as a buffer to maintain over actual memory requirements, you can configure Hyper-V to grow and shrink RAM allocations as virtual machines require. This means you could give a virtual machine 2GB of RAM, but allow it to grow up to 4GB as needed. If the VM needs less, Hyper-V can then reduce physical RAM usage on the host. In situations where a host exhausts physical RAM, Hyper-V will begin reducing the allotted RAM to running virtual machines based on their priority.

Like memory management in VMware's hypervisor, Hyper-V's dynamic memory allows you to run a higher density of VMs on each host. Microsoft's method of memory allocation, which utilizes a memory balloon that can expand and contract as needed, has clear benefits, but doesn't go as far as VMware's or Red Hat's, which leverage advanced features such as page sharing and RAM compression. Plus, Hyper-V's dynamic memory works only with Windows guests; VMware and Red Hat have no such limitation.

Hyper-V R2 installation
Installing and configuring a Hyper-V cluster is not as straightforward as implementing the VMware, Red Hat, and Citrix solutions. One reason is that installation of hosts and VMs are handled by separate tools in the case of Hyper-V, but are combined in the other solutions.

Another reason is that some of the foundational pieces for Hyper-V are borrowed, such as the use of Microsoft Cluster Services to handle a farm of Hyper-V servers. Although it may seem to make sense to repurpose these existing tools in the virtualization realm, there are inherent drawbacks. Due to odd dependencies, cluster heartbeat configuration, storage and network configuration, and other administration tasks become cumbersome and time-consuming, and initial builds require plenty of repetitive manual steps on each host to get to a stable cluster. Also, the limit of 16 nodes in a cluster may be a problem for larger shops.