Virtualizing Exchange 2007 and Exchange 2003 with Hyper-V

For a long time I chose not to use virtualization technology in my Microsoft Exchange Server environment because I didn't want to add an extra layer of abstraction to the mix. Plus, I knew that my servers would perform better on dedicated hardware.

Over the past couple of years, though, virtualization technology has improved tremendously. Thanks to Microsoft Hyper-V, virtual machines can directly access most of a server's hardware rather than having to channel requests through the host OS as was previously required. Because Hyper-V offers better performance than Microsoft's previous virtualization products, I have virtualized my own Exchange servers and have assisted some of my clients in doing the same.

Should You Virtualize?
Microsoft supports virtualization in Exchange Server 2007 and Exchange Server 2003 but not earlier versions. Virtualization is mainly used in production environments to make better use of existing hardware. For example, DNS, DHCP, and file servers use very little of the available memory and CPU resources. By virtualizing these types of servers, you can use a single physical machine to host multiple virtual machines. In doing so, the hardware is being better utilized and fewer resources go to waste.

Virtualization typically isn't well suited for servers that use a lot of CPU or disk resources. Unfortunately, in many cases, Exchange falls in this category. If you're thinking about virtualizing an existing Exchange server, it's important that you do some performance benchmarking to find out how much of the server's resources are being consumed during peak periods of activity.

Virtualization adds an extra layer of abstraction to the process. As a result, virtual servers take a performance hit. I can't tell you exactly how much of a performance hit to expect because it depends on a number of factors, such as the virtualization product being used, the available hardware resources, the load that other virtual servers are placing on the hardware, and how efficiently the guest and host OSs are configured.

Which Virtualization Software Should You Use?
You can use Hyper-V or third-party software to virtualize Exchange 2007. For Exchange 2003, you can use Microsoft Virtual Server 2005 R2 or third-party software. Although Microsoft doesn't officially support using Hyper-V with Exchange 2003, I've found that it works really well.

Although Microsoft typically discourages customers from using third-party virtualization software, they support doing so in some cases. VMware's ESX Server is one such case. For more information about running Exchange on third-party virtualization products, read "Support policy for Microsoft software running in non-Microsoft hardware virtualization software."

I recommend that you host your virtual Exchange 2007 servers on Hyper-V. I also recommend that you use Hyper-V for your Exchange 2003 servers for two main reasons:

• The virtualization process in Hyper-V isn't nearly as dependent on the host OS as the virtualization process in Virtual Server 2005. Hyper-V supports hardware-level virtualization, which means virtual machines are allowed to communicate directly with the server's hardware instead of hardware calls having to be passed through the host OS. The end result is that virtual machines perform almost as well as physical machines.
• When you use Virtual Server 2005, the virtual machines can use only one processor. If your Exchange server is currently running on a multi-CPU or multi-core server, you might see the server's performance diminish considerably once you move to a virtual environment. This constraint has been removed in Hyper-V. You can assign multiple virtual CPUs to a virtual server. You can even manually assign virtual CPUs to an Exchange server and any other virtual servers on the machine to avoid situations in which a virtual server doesn't receive sufficient CPU resources because another virtual server is hogging the CPU.

Note that an Exchange server must have x64 processors that support hardware-level virtualization to use Hyper-V. Intel and AMD offer processors with this support. In Intel processors, the support is called Intel Virtualization Technology (Intel VT).  In AMD processors, the support is called AMD Virtualization (AMD-V).

Microsoft offers two Hyper-V products: Windows Server 2008 Hyper-V, which is a role in Windows Server 2008, and Microsoft Hyper-V Server 2008, which is a standalone server-virtualization product that you can download from the Microsoft website for free. Hyper-V Server 2008 doesn't include the Server 2008 OS or Server Core. (For more information about the differences between these two products, see "What You Need to Know About Microsoft Hyper-V Server 2008.") You can use either Hyper-V product when virtualizing Exchange.