Microsoft recently made changes to its licensing program for Microsoft Server Products in Virtual Environments. My colleagues, Chris Wolf and Richard Jones, commented on the changes in licensing from the data center perspective. However, as part of the announcement, Microsoft also published a support statement for virtualizing Exchange. While the statement is very detailed, it led me to an important question for Microsoft – or as one of the Microsoft folks I talked with aptly put it: “This announcement begs the question of whether MSFT recommends virtualizing the Mailbox server role.”

The answer? “The answer is that while the Mailbox server role is supported in a virtual environment and customers are permitted to do it, we generally recommend customers run Mailbox servers on physical hardware.” 

The reasons are understandable – Mailbox servers have high server transactional costs that lead to high CPU utilization, heavy disk IO, and large quantities of attached data. 

The support statement doesn’t contain this advice, so after further conversation with the folks at Microsoft, I received the following clarifications: 

  • Virtualizing Exchange in test, development, or small deployments (branch office, for example) is not a bad idea because the load is lighter.
  • The role of the Exchange server needs to be considered – a mailbox server is a role where issues may arise, but an edge transport or client access server might be a good candidate, depending upon the architecture of the implementation.
  • You can throw more hardware power at the mailbox server role, depending upon the load, but the drawback may be that you end up paying more for the hardware than if you didn’t virtualize.  The mathematics of the TCO need to be examined in this scenario.
  • Virtualizing Exchange narrows your storage options, like deploying on a SAN, and may force smaller mailbox quotas. 
  • Avoid the mistake of making the virtualized Exchange a single point of failure. 
  • Note that support for virtualized Exchange 2007 is for SP1 or better.  The Microsoft folks verified that this is not because of specific fixes in SP1, but rather to take advantage of the fact that 2007 SP1 is the version supported on Windows Server 2008 with Hyper-V. 

The folks at Microsoft offered some recommendations for virtualized Exchange also:

The sum? Virtualizing production Exchange mailbox servers is, generally, not a good idea from a technical perspective. When I asked the folks at Microsoft if they were going to use virtualization for Exchange Online, their answer was no.They said it would increase their management load and tweaking Exchange and AD to run multi-tenant was more cost effective.