Released: Exchange 2013 Server Role Requirements Calculator
Published May 14 2013 06:00 AM 345K Views

To download the calculator, please see the attachment on this post (also note that the calculator can be used for E2016 deployments as per this).

It’s been a long road, but the initial release of the Exchange Server Role Requirements Calculator is here. No, that isn’t a mistake, the calculator has been rebranded.  Yes, this is no longer a Mailbox server role calculator; this calculator includes recommendations on sizing Client Access servers too! Originally, marketing wanted to brand it as the Microsoft Exchange Server 2013 Client Access and Mailbox Server Roles Theoretical Capacity Planning Calculator, On-Premises Edition.  Wow, that’s a mouthful and reminds me of this branding parody.  Thankfully, I vetoed that name (you’re welcome!).

The calculator supports the architectural changes made possible with Exchange 2013 and later:

Client Access Servers

Like with Exchange 2010, the recommendation in Exchange 2013 is to deploy multi-role servers. There are very few reasons you would need to deploy dedicated Client Access servers (CAS); CPU constraints, use of Windows Network Load Balancing in small deployments (even with our architectural changes in client connectivity, we still do not recommend Windows NLB for any large deployments) and certificate management are a few examples that may justify dedicated CAS.

When deploying multi-role servers, the calculator will take into account the impact that the CAS role has and make recommendations for sizing the entire server’s memory and CPU. So when you see the CPU utilization value, this will include the impact both roles have!

When deploying dedicated server roles, the calculator will recommend the minimum number of Client Access processor cores and memory per server, as well as, the minimum number of CAS you should deploy in each datacenter.


Now that the Mailbox server role includes additional components like transport, it only makes sense to include transport sizing in the calculator. This release does just that and will factor in message queue expiration and Safety Net hold time when calculating the database size. The calculator even makes a recommendation on where to deploy the mail.que database, either the system disk, or on a dedicated disk!

Multiple Databases / JBOD Volume Support

Exchange 2010 introduced the concept of 1 database per JBOD volume when deploying multiple database copies. However, this architecture did not ensure that the drive was utilized effectively across all three dimensions – throughput, IO, and capacity. Typically, the system was balanced from an IO and capacity perspective, but throughput was where we saw an imbalance, because during reseeds only a portion of the target disk’s total capable throughput was utilized. In addition, capacity on the 7.2K disks continue to increase with 4TB disks now available, thus impacting our ability to remain balanced along that dimension. In addition, Exchange 2013 includes a 33% reduction in IO when compared to Exchange 2010. Naturally, the concept of 1 database / JBOD volume needed to evolve. As a result, Exchange 2013 made several architectural changes in the store process, ESE, and HA architecture to support multiple databases per JBOD volume. If you would like more information, please see Scott’s excellent TechEd session in a few weeks on Exchange 2013 High Availability and Site Resilience or the High Availability and Site Resilience topic on TechNet.

By default, the calculator will recommend multiple databases per JBOD volume. This architecture is supported for single datacenter deployments and multi-datacenter deployments when there is copy and/or server symmetry. The calculator supports highly available database copies and lagged database copies with this volume architecture type. The distribution algorithm will lay out the copies appropriately, as well as, generate the deployment scripts correctly to support AutoReseed.

High Availability Architecture Improvements

The calculator has been improved in several ways for high availability architectures:

  • You can now specify the Witness Server location, either primary, secondary, or tertiary datacenter.
  • The calculator allows you to simulate WAN failures, so that you can see how the databases are distributed during the worst failure mode.
  • The calculator allows you to name servers and define a database prefix which are then used in the deployment scripts.
  • The distribution algorithm supports single datacenter HA deployments, Active/Passive deployments, and Active/Active deployments.
  • The calculator includes a PowerShell script to automate DAG creation.
  • In the event you are deploying your high availability architecture with direct attached storage, you can now specify the maximum number of database volumes each server will support. For example, if you are deploying a server architecture that can support 24 disks, you can specify a maximum support of 20 database volumes (leaving 2 disks for system, 1 disk for Restore Volume, and 1 disks as a spare for AutoReseed).

Additional Mailbox Tiers (sort of!)

Over the years, a few, but vocal, members of the community have requested that I add more mailbox tiers to the calculator. As many of you know, I rarely recommend sizing multiple mailbox tiers, as that simply adds operational complexity and I am all about removing complexity in your messaging environments. While, I haven’t specifically added additional mailbox tiers, I have added the ability for you to define a percentage of the mailbox tier population that should have the IO and Megacycle Multiplication Factors applied. In a way, this allows you to define up to eight different mailbox tiers.


I’ve received a number of questions regarding processor sizing in the calculator.  People are comparing the Exchange 2010 Mailbox Server Role Requirements Calculator output with the Exchange 2013 Server Role Requirements Calculator.  As mentioned in our Exchange 2013 Performance Sizing article, the megacycle guidance in Exchange 2013 leverages a new server baseline, therefore, you cannot directly compare the output from the Exchange 2010 calculator with the Exchange 2013 calculator.


There are many other minor improvements sprinkled throughout the calculator.  We hope you enjoy this initial release.  All of this work wouldn’t have occurred without the efforts of Jeff Mealiffe (for without our sizing guidance there would be no calculator!), David Mosier (VBA scripting guru and the master of crafting the distribution worksheet), and Jon Gollogy (deployment scripting master).

As always we welcome feedback and please report any issues you may encounter while using the calculator by emailing strgcalc AT microsoft DOT com.

Ross Smith IV 
Principal Program Manager
Exchange Customer Experience

Version history
Last update:
‎May 13 2020 11:33 AM
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