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As part of your Exchange 2010 planning process, one of the areas you must focus on is the Mailbox server design. One component in that design process will be determining your CPU requirements. To that end, we have published guidance that identifies the megacycles / mailbox for each message profile that exists, for both active and passive mailboxes. This data was collected using a baseline system (2x4 core Intel Xeon x5470 3.33-GHz processors that yields 3333 megacycles per processor core, with a SPECint2006 rate value per core of 18.75). Most of you, however, will not be deploying Exchange 2010 on the same hardware that we used to collect this data; therefore, you must perform a megacycle adjustment to determine the available megacycles your server design can support.
Recently we made a change with respect to how we normalize the available megacycles of server platforms with respect to our baseline system. Initially, we adjusted megacycles per core with respect to the total megacycles of the system and derived this formula:
((New platform per core value) * (Hertz per core of new platform)) / (Baseline per core value) = Adjusted Megacycles per Core
However, that is not the correct way to look at normalizing the server platforms against our baseline. What we are actually interested in is how this impacts the active mailbox user count. Therefore the new formula is:
((New platform per core value) * (Hertz per core of baseline platform)) / (Baseline per core value) = Adjusted Megacycles per Core
To understand this change, let’s look at an example solution that utilizes an 8 core x5550 2.66GHz (2660 megacycles/core or 21280 megacycles) processor architecture that has a SpecInt2006 rate value of 30.12 per core.
However, if you look at this from the mailbox perspective, you get the following (assume 200 message profile, so 4 megacycles / active mailbox):
If we refer back to our SpecInt2006 rate value, the difference between the baseline system and this example system is 60%. Therefore, the formula that needs to be used to determine the adjusted megacycle per core value is:
((New platform per core value) * 3333) / 18.75 = Adjusted Megacycles per Core
This guidance change is effectively immediately and is documented within the TechNet article, Mailbox Server Processor Capacity Planning. The documentation within the Exchange 2010 Mailbox Role Requirements Calculator will also be updated to reflect this.
For those of you that have already sized your systems using the old, invalid formula, don’t panic, your systems simply will have some extra megacycle capacity. The extra amount will depend on the difference between the MHz value of your processor and the baseline value of 3333 MHz.