“The more the better,” is a common mantra when it comes RAM but, in the case of Exchange Server 2007, that’s certainly not the case (OK, so it isn’t really the case in relation to other operating systems either, but that’s for another story).

With Exchange Server, Microsoft recommend no more than 32 GB of RAM. That’s because a) more than 32 GB will not substantially improve performance (and so you’d be wasting your money) and b) it may actually negatively impact performance. Here’s why (from Microsoft):

Cold state is defined as the state of the Mailbox server immediately following a server reboot or store.exe process restart. The Database Cache, which is used to cache database read/write operations, is small in size (or “cold”) during this period so it has a significantly diminished ability to reduce read I/O operations. As the Mailbox server processes messages, the Database Cache Size grows which increases the effectiveness of the cache and subsequently reduces the I/O footprint of the server. The larger the physical memory size of the server the longer it takes the Database Cache size to reach its optimal size. If the storage is designed/sized for a server with a large amount of physical RAM (>32GB), and the I/O profile of the users assumes an optimal Database cache state (large/warm cache); then the client experience may be compromised due to insufficient disk performance during these “cold state” periods.

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