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We got this question at our TechNet Event back in January. The person didn’t give their name, so let’s call him Jooblety-Goop.
“Dynamic Memory and Exchange 2010 - What happens in that scenario?”
Well JG, I assume you’re asking about how Exchange Server 2010 works as a virtual workload (Short answer: Just great!), and more specifically if there is anything special about how (or if) virtualized Exchange Servers can take advantage of Hyper-V Dynamic Memory. (For those of you not familiar with what Dynamic Memory is, check out the first few pages of this Dynamic Memory Whitepaper.)
Dynamic memory is great for adjusting the memory used by a virtual machine when the need for additional memory is temporary, and when there are no applications that are tuned to assuming a certain pool of memory will simply be there continuously. Unfortunately (or fortunately, depending upon which product group you work for), applications like Exchange Server and SQL Server (and many others, I’m sure) grab as much much memory as possible right up front (I may be oversimplifying, but this is basically the idea) in order to manage their memory pool in the way that best suits their needs, or tuned for performance given the existing limits of the hardware. That’s really smart; but it also means that they simply work better when they can depend upon a fixed set of memory to work with. A sudden change in the amount of memory available can actually have a negative impact on performance.
So the recommendation for Exchange Server 2007 and 2010 running on top of Hyper-V R2 w/SP1 is that you do not take advantage of Dynamic Memory for those virtual machines.
Here are some additional resources on the topic:
Understanding Memory Configurations and Exchange Performance – to understand, you know, the memory configurations and, like, how performance of, say, Exchange Server is impacted.
Microsoft Support Policies and Recommendations for Exchange Servers in Hardware Virtualization Environments – Recommendations of support policies from Microsoft for how, like, Exchange Server will work on, you know, environments of virtualized hardware.
Hyper-V Dynamic Memory Configuration Guide – to guide you, you know, through the configuration of dynamic memory in Hyper-V.
(In case you haven’t noticed, I have been, like, you know, talking with my teenage daughters a lot lately, and it’s, like, rubbing off.)
And huge props to the Hyper-V.Nu blog for this post, which lead me to personally understanding this topic better. Nice work!
How are you configuring virtualization to handle your Exchange workloads? Let us know in the comments!
Another good link (for SQL) is "Running SQL Server with Hyper-V Dynamic Memory, Best Practices and Considerations" at: msdn.microsoft.com/.../hh372970.aspx