Exchange 2013 Sizing — Tips and Tricks Part 3

In our previous episodes, we discussed the basics of sizing your Exchange 2013 deployment, including determining the various vital stats for calculating Exchange 2013 mailbox server resource requirements.

Let’s continue by reviewing our results and determining if they accurately meet the “reality” of the e-mail system to be upgraded.


Along with other system-wide settings, we determined the following key utilizations of our sample Exchange 2010 system:

  • 11,000 users, divided into tiers of:
    • Tier 1
      • 1,000 users
      • 5% user growth
      • 2200 MB initial mailbox size = 2 TB total
      • 4096 MB mailbox limit
      • 100 KB average message size
      • 50% of users with ActiveSync and Outlook clients running concurrently
    • Tier 2
      • 4,000 users
      • 5% user growth
      • 1050 MB initial mailbox size = 4TB total
      • 3072 MB mailbox limit
      • 75 KB average message size
      • 50% of users with ActiveSync and Outlook clients running concurrently
    • Tier 3
      • 6,000 users
      • 5% user growth
      • 125 MB initial mailbox size = .70 TB total
      • 500 MB mailbox limit
      • 50 KB average message size
      • No mobile device usage

The Exchange Resource Calculator takes all of your inputs, and generates Exchange server sizing.

You might be tempted to say “hey, let’s take that to our CIO and ask for the $$$.”  However, let’s review the results and see how “real” they are.


Review the Recommended RAM Configuration and Processor Cores Utilized and compare to your existing system.  Note that in our case the calculator is calling for 256 GB of memory and 31 processor cores.  Keep in mind that with server role consolidation, the Exchange Server that was doing nothing but mailbox tasks in Exchange 2007 or 2010 is now doing various client access and mail routing activities, which can account for the increased per server resource requirements.  Additionally, memory use in Exchange 2013 is determined by the amount of daily messages sent/received, so adjust this input if the recommended memory allocation(s) seem wrong.

Also note that we’ve configured the calculator to use only 1 Exchange server; we’ll be altering the configuration shortly to better fit within Microsoft’s single server scalability best practices.


Next, study the recommended disk storage requirements, for both GB and IOPS.  The calculator provides recommendations for the following storage uses:

  1. Transport database
  2. Mailbox databases
  3. Transaction logs
  4. Restore volume


Determining a data storage design for an Exchange 2013 upgrade can be a drama-inducing event, due to actual and/or perceived cost of storage for Exchange deployments.  The various optimizations in the Exchange mailbox databases have definitely resulted however in dramatic changes in performance requirements.  Deployment of Exchange databases on 7200 rpm SAS drives, the use of internal or direct-attach storage, and JBOD storage architectures all result in a more cost efficient design than in previous years, while still meeting system performance requirements.


Note that the Role Requirements tab of the calculator in our example above is saying “buy 36 TB”.  However, this calculation is taking into account the Projected Mailbox Number Growth Percentage and Mailbox Size Limit entered into the mailbox tier settings on the Input tab.  Taking all of that into account, plus the additions for volume free space, indexing space, and deleted items retention space, you will probably get a recommendation somewhat above your current Exchange server disk space allocation.


To better define your storage requirements, perform a “top down” calculation and compare it to the Exchange Resource Calculator’s results.  I like to do this via a simple spreadsheet, starting with total amount of mail content in the databases (not including white space), increases in mailbox size and count, and then adding adjustments for deleted items retention, volume free space, DB overhead space, and indexing space.  Lastly we add on the recommended transaction log and restore volume space, and compare our total to the Calculator’s total.

Our results are below.  Note that it totals to around 35TB; we’re not looking for an exact match here, just +/- a few TB to either verify or not that the Calculator results are realistic .  When it comes to finalizing the final server and storage purchase/design, use the results from the Calculator.


Next up in part 4, IOPS and enabling the Calculator settings to determine server sizing in a high availability/disaster recovery deployment.

Planning an Exchange Server upgrade and looking for design assistance?  Let’s talk.

Phone: 312-602-4000
222 W. Adams
Chicago, IL 60606
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