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A commonly repeated adage about Exchange Server memory is "more is better." The more memory you have, the less likely Exchange Server will experience bottlenecks and the faster things will run.
Exchange 2007 is all the more powerful on systems with more than 4 GB of RAM, thanks to its 64-bit architecture. So it would seem to make sense to throw as much memory as is physically possible at a given 64-bit Exchange installation, right?
That's the theory, but the practice -- especially when it comes to Exchange Server 2007 -- is a little different.
In Microsoft's article about Exchange Server 2007 hardware, "Planning processor and memory configurations," there are a number of surprises regarding the best memory configurations for a 64-bit Exchange installation. One is the revelation that 32 GB is the most cost-effective memory configuration for Exchange 2007 boxes.
This is not a limitation of Exchange 2007, but an observation about how cost-effective that much memory in a given Exchange Server will be, and how expensive it is to buy the required hardware.
An Exchange 2007 system's memory bus architecture may impose speed limits based on how much memory is installed. A system with 16 GB of PC3200 memory can support 32 GB of memory, but only at PC2700 speeds (so having more memory may be offset by the fact that it's slower).
Another hardware consideration is that a given Exchange 2007 server may work better when more memory slots are filled vs. having denser memory modules in fewer slots.
Microsoft breaks down recommended memory allocations for Exchange 2007 servers based on their roles. For example, a mail server will probably need 2 GB plus 2 MB to 5 MB per mailbox, with a recommended maximum of 32 GB.
There are two caveats:
- These estimates don't take into account third-party applications that might be running on the same Exchange server.
- It assumes fairly sane mailbox usage -- i.e., you're not allowing people to have 5 GB mailboxes or something equally absurd.
For my own edification, I went to Dell's site to spec two separate servers: one that scaled to 64 GB of RAM and another that only scaled to 32 GB. The first had memory speeds that topped out at 400 MHz (DDR2). The second went up to 667 MHz (DDR2) and started at far less of a price.
About the author: Serdar Yegulalp is editor of Windows Insight, a newsletter devoted to hints, tips, tricks, news and goodies for all flavors of Windows users.
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