Why would you want to run Exchange Server in a virtualized environment? The simple answer is flexibility. Putting the Exchange server into a virtual infrastructure lets you run a common set of hardware drivers on all of your servers. This creates an easy way to use a standard OS build.
When the Windows operating system is a single file that's under the control of the virtualization software, you can also move the guest system between hosts if there is a problem with the host server. To clarify, a host server is the physical server doing the virtualization; a guest is the server being virtualized. If a guest system running on the host needs additional processing capability, such as end-of-the-month financial runs, for example, it or other guests can be moved onto other hosts that have spare processing power or memory.
When planning an Exchange Server 2007 infrastructure on physical hardware, you can maximize the investment by hosting as many users as possible on the Exchange 2007 Mailbox server. In a virtualized situation, it pays to run several small Exchange servers because mailbox servers with a smaller footprint can be moved between hosts easily. Having a monolithic Exchange Server guest restricts your ability to move it from host to host server, when needed.
Does this mean you're investing in more Microsoft Exchange licenses than necessary? Yes, to an extent. However, you are saving a lot of money on hardware; giving yourself the capability to adjust Exchange Server performance on the fly; and gaining a disaster recovery solution, or at the very least, a high availability solution. The final costs might be the same, but you get a better infrastructure for the money.
You could end up with the same number of Windows licenses used previously. Running Windows in a virtualized environment allows you to run several instances of Windows in guests on physical hosts for the cost of a single Enterprise edition license. Visit Microsoft's website for complete licensing details.
Architectural decisions are impacted as well. For example, with VMware, you're less likely to implement cluster continuous replication (CCR), but may still want to use standby continuous replication (SCR).
If your storage cannot replicate database LUNs efficiently, it may best to implement SCR. Currently, Microsoft's Hyper-V doesn't offer an equivalent solution to VMware HA, so using CCR in this situation is a better option. Whether to run SCR or not will depend on your data center choices and service-level agreements (SLAs).
Virtualization and Exchange server roles
The Mailbox Server role isn't the only role within Exchange Server 2007 that can benefit from virtualization. The Hub Transport role is a potential point of failure in an Exchange organization. For example, a site failure occurs and an active CCR node must either rely on a passive CCR node in another data center across the WAN or, rely on a remote SCR node. If the original data center is unreachable, there could be a significant amount of email stranded on the active CCR node that the passive node or SCR server must transfer from the Hub Transport.
If the Hub Transport server is unavailable, then messages are lost instantly. The replication capabilities available in a storage area network (SAN) enable you to bring up the guest image at the remote data center. The activated mailbox server then can access the missing email from that replicated hub transport guest server and deliver it to the local database.
Client Access servers (CAS) can also benefit from virtualization. These servers can redirect and proxy, which determines whether the user should go through that CAS or be redirected to a more appropriate CAS upon initial contact. This is based on parameters that the administrator set with regard to your knowledge of the physical network.
Pre-positioned physical CAS systems spread over data centers may not immediately route or redirect users correctly. Administrators also must watch the configuration of those servers. When a virtualized CAS guest is activated and communicating with the mailbox nodes, users should experience a seamless application transfer. However, this will only occur if your network and dependent Active Directory (AD) infrastructure have been properly configured.
Although it's still an unsupported configuration, virtualizing Microsoft Exchange 2007 servers gives an organization another weapon in its high-recovery arsenal. Virtualization is not for everyone; really large organizations will have enough users to completely fill many large Exchange servers to capacity. They also have the funds available to SAN-boot Exchange servers and bring a spare server online.
Smaller organizations, however, can benefit from virtualizing single Exchange servers with directly connected disks. It's up to these individual companies to look at virtualization and determine whether to do a partial or full-blown implementation.
About the author: Mark Arnold, MCSE+M and Microsoft MVP, is Principal Consultant with LMA Consulting LLC, a private messaging and storage consultancy based in Philadelphia, Penn. Mark assists customers in designs of SAN-based Exchange Server implementations. He has been a Microsoft MVP in the Exchange discipline since 2001, contributes to various Microsoft-focused technology websites, and can be found in the Exchange newsgroups and other Exchange forums.
There is a consideration that author Mark Arnold failed to include in his article. Microsoft does not support Exchange Server 2007 on any virtualization platform other than Windows Server 2008 with Hyper-V. Microsoft support on non-Microsoft virtualization platforms is very limited. This is a very important factor when planning any Exchange virtualization design strategy.
Please be sure to inform your readers of this information:
Yes, Rik. You are correct. When this article was written, Microsoft's support policy was limited. However, Microsoft had announced that it was working on a new support policy for virtualized Exchange Server environments. Recently, Microsoft released this new support policy, which includes support for third-party Exchange virtualization platforms.
Please read Exchange virtualization expert David Davis' column on how Microsoft's new support policy for virtualized Exchange Server will affect you.
—Kimbers Sheppard, Site Editor, SearchExchange.com
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