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How to calculate Exchange 2013 resource requirements
Inadequate server resources can impair performance and growth. Here's how to calculate megacycles of work and memory requirements for Exchange 2013.
Are you sabotaging your Exchange Server's performance? You might be if you haven't implemented the right storage for your setup.
Not taking a thorough look at your server can cause problems later on. Performance issues from Exchange 2013 deployments often relate to storage, such as disk characteristics, capacity and volume-based features and functionality.
No discussion of Exchange performance is complete without a computing resources sanity check.
Calculate megacycle requirements
Exchange processors are expressed in terms of megacycles of work, so results may be convoluted. One megacycle is approximately a single 1 megahertz (MHz) processor working for one second. But today's processors run at 2,000 MHz to 3,000 MHz or more. Advanced processor instruction sets and features make handling Exchange workloads more effective than the basic megacycle figure might indicate.
For a more accurate number of required megacycles, use a benchmarking tool that correlates the processor's precise performance score to megacycles, such as the Exchange Processor Query Tool.
For simplicity, let's say that 1 gigahertz (GHz) is 1,000 megacycles. If you have a 12 core server running at 2.8 GHz, you'd have about 33,600 [12 x 2,800] megacycles to work with.
Next, figure out how many megacycles you need. One rule of thumb is roughly 0.043 megacycles per message per mailbox for each day for a standalone mailbox server. If you have one mailbox exchanging 50 messages each day, you need about [50 x 0.043] 2.15 megacycles.
If you have 100 mailboxes exchanging 150 messages per day, plan on about 645 megacycles [150 x 0.043 x 100]. If you have 1,000 mailboxes exchanging 300 messages per day, figure about 12,900 [300 x 0.043 x 1,000] megacycles.
In each case, the 12 core server should be adequate. Exchange architects usually drive server loads up to 80% (about 26,880 megacycles) without problems.
Get help with tools
Exchange 2013 is a demanding business application and imposes substantial loads on storage and server computing resources. Proper sizing and configuration is essential, not just for the initial deployment, but for message traffic and end user growth throughout the Exchange lifecycle. But sizing and configuration can be complex issues.
Tools such as the Exchange 2013 Server Role Requirements Calculator version 6.6 can help organize and simplify the sizing process. Simplifying the process offers a better estimate of resources Exchange performance across a wide range of roles and reduces wasted capital in server or storage purchases.
Calculate memory requirements
Although the minimum memory required is 8 gigabytes (GB), the total memory requirement for Exchange services, caching, content indexing and other related tasks can add up quickly and cause a substantial memory footprint.
The rule of thumb here is about 0.24 megabytes (MB) per message per mailbox per day on a single mailbox server. If a mailbox exchanges 250 messages per day, plan to provide 60 MB [250 x 0.24 MB] for that mailbox user.
To calculate memory, multiply the number of databases by the number of end users per database, then by space per mailbox. For example, if the server has a minimum of 32 databases with 80 end users per database (up to 2,560 end users), each exchanging 200 messages per day, the required memory is about 122,880 MB [(32 x 80) x (200 x 0.24)], or about 128 GB.
