Released: Exchange 2013 Server Role Requirements Calculator

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

Comments (52)
  1. Ratish Nair says:

    terrific !!! been waiting for a while…

  2. It is so shiny and still has that new calculator smell to it. <breathes in deep> Ahhhhhh.

  3. Samuel says:

    Awesome! Can't wait to have a test!

  4. Very cool! It was a long wait but it prooved to be worth it. Thanks a ton!

  5. says:

    long awaited and appreciated!!!

  6. M.Gamal says:

    Great news !

  7. Robert says:

    This is great but when is the storage calculator going to be released for 2013?  

  8. @Robert: This is the Exchange 2013 calculator.  :-)

  9. Bernd Kruczek says:

    Do we now have tu use the accurate calculator for Exchange 2010 or 2013?


  10. @Bernd, you use the calculator from this blog post with Exchange 2013.  You use the older calculator at with Exchange 2010.

  11. says:

    Excellent, thank you

  12. Chin3 says:

    How about Disk Space for OS and Installation ? Do we have to calculate it manual ?

  13. Matt Fletcher says:

    Thanks for this, good job.  I've watched Scott's 2012 New Zealand TechEd sessions which include HA and Site resilience topic on Channel9, I believe it was for pre RTM,   just wanted to say how awesome they are.  Many thanks and I'm looking forward to watching the North American TechEd, in case there's more cool new features for CU1.

  14. PrabhatNigam says:

    Awesome!!! World was holding the deployment for this

  15. says:

    Yes, great work! I'm going to check our current implementation immediately. :-)

  16. Dame Luthas says:

    Thanks Gentlemen, Any word on the release of the updated Exchange Client Network Bandwidth Calculator?

  17. says:

    Question on the calculator. When I do a configuration for 200 Mailboxes(2 databases with 100 mailboxes on each.), Do I really need 24GB of memory on each database server?

  18. says:

    I am really glad to see this.

  19. Gengaiyan_1 says:

    Traffic improvement, I do checking now….Thanks for your support engineers

  20. Great Work Gents ;-)

  21. pesospesos says:

    Exciting!  Ross is there any forthcoming info on UM migrations?  The current TechNet article is confusing and seems to contradict itself in the early steps:…/dn169226(v=exchg.150).aspx


  22. says:

    Pesos – I'm willing to help here with UM, but I'm not sure what you're asking.  Can you give me some details? Thanks.

  23. NathanHD says:

    Oh my golly gosh! Thankyou. Orin Thomas just gave me the very exciting news during a class.

  24. Bernd Kruczek says:

    @ Scott Schnoll

    Does that mean that the Calculator for Exchange 2010 will not be updateted in the future and that calculator fpr Exchange 20010 will not be developed further?


  25. @Bernd, no.  There are two calculators.  One for Exchange 2013, and one for Exchange 2010.

  26. @Bernd – In fact, I will be releasing an updated E2010 calc soon.  I've been holding off on it as I knew a certain grumpy Irishman and a few other folks would have commented on the release of an existing calculator when the E2013 wasn't out yet. :)


  27. says:

    Thanks for the calculator. It's given me some guidance for our upcoming deployment. However, I am having an issue on the distribution tab. When I click on the Calculate button, I get runtime error "11", "Division by zero" and it clears everything from the page. Am I doing something wrong?

  28. pesospesos says:

    @Tony – thank you for helping with UM!  Perhaps you can chime in on my thread here on the forums; looking forward to completing this migration!…/32bd9392-4f9a-4acf-b086-6d2e0fc58bdb

  29. @Eric – please send a copy of the calculator to the email address listed in the article.

  30. GMT says:


  31. Customer says:

    Hi, I got the same issue as Eric McAnallen.

  32. says:

    Great Work.

    I want to inform you that the distribution sheet is not working correctly on one of my inputs. When I select two servers at primary site and one at secondary site the distribution sheet open a debug window. Can you please check and confirm if the calculator is working fine.


  33. Julien Taisne says:

    Hi Ross,

    First, thanks for this amazing job !

    Can you tell me about the "Recommended Min Number of GC Cores" ?

    The value should be about "Exchange servers Core Number" / 8, isn't it ?

    Refering to :…/ask-the-perf-guy-sizing-exchange-2013-deployments.aspx

    "Active Directory sizing remains the same as it was for Exchange 2010. As we gain more experience with production deployments we may adjust this in the future. For Exchange 2013, we recommend deploying a ratio of 1 Active Directory global catalog processor core for every 8 Mailbox role processor cores handling active load, assuming 64-bit global catalog servers."

    The storage Calculator, in our sizing environement, gives us a 51/1 result, there is maybe a mistake ?



  34. @Julien Taisne:

    When you calculate required GC cores, the ratio 1:8 applies to the cores required to support active mailboxes ("Mailbox role processor cores handling active load") and not to all cores physically available on Exchange server.

    So, for example, if you have 32 total cores on an Exchange server but only 16 of them are actually needed to support active mailboxes (as determined by the calculator), you will need only 16/8=2 GC cores to support this Exchange server's AD queries.

    I hope this clarifies your question.

  35. Mike DiVergilio [COX] says:

    Since you cannot override the RAID settings when using 7.2K RPM drives, does this imply that Microsoft does not support that configuration? TechNet states you support all RAID types, but the calculator doesn't give you the latitude to make that decision. While you prefer RAID 1/0 when using slower disks, certain storage vendors have capabilities in the array that can offset some of the performance implication, such as storage pools, thin provisioning and fast cache.

  36. Jesse Sutela says:

    POSSIBLE BUG??:  It seems like the calculator is taking my tier 3 mailbox count and multiplying it by 6 in the role requirements tab.  I put in 1000 and it shows as 6000.  

  37. Jesse Sutela says:

    Never mind on the bug….  Not a bug.  Growth %

  38. julien says:

    @ Boris Lokhvitsky

    Thanks for your reply, indeed we've finaly find this ratio after some test with the storage calc.


  39. says:

    In the "Role Requirement" sheet -> Server configuration section ->the value for Recomended RAM configurattion – Is it per server or per data center ? eg: if the value of recommended RAM is showing as 96 GB of RAM , and I have 2 servers in the primary datacenter , does it mean , each server should have 96/2 = 48 GB RAM ?

  40. @Mike – There are no plans to change the calculator to support RAID-5/6 with 7.2K disks.  While it is supported to deploy our testing in the past as shown that JBOD and RAID-1/0 deployments to be more suitable.

    @Bineesh – RAM is per server.

  41. Robert says:

    VBA Code Nags…

    Option Explicit should be everywhere  (missing on the forms and code behind the worksheets)

    Constants should be explicitly typed (otherwise they are variants)

    Use Longs instead of Integers

    Password protect the code (even though easily hacked)?

  42. Andy Walker says:

    Awesome, just in time for my current 2013 hybrid engagement :-)

  43. Andrew Mead says:

    Question on some calculator results I'm seeing after hearing your presentations at TechEd…

    Looking at the differences between selecting Site Resilient Deployment = Yes with 2 CAS/MB multi-role servers in the primary datacenter, and 2 in the secondary datacenter in an active/active single DAG deployment.

    With our settings, the role requirements indicate 96GB RAM for each of the 4 servers, in order to support losing both servers in either datacenter.

    If I run the same settings against Site Resilient Deployment = No, still keeping a single DAG with 4 multi-role CAS/MB servers, allowing for the failure of any 2 of the servers (in the same datacenter), the calculator indicates 48GB RAM required.

    I'm missing what the "special sauce" is in a Site Resiliency scenario that would necessitate double the RAM.  In the site resiliency scenario, both datacenters are hosting 50% of the active user databases, so the servers are carrying the same 25% load in both cases in normal operation, with the possibility of hosting up to 50% of the load, should both servers in the other location fail.

    In our case, our secondary datacenter is directly fiber connected and is essentially a remote extension of our primary datacenters, so while in a different subnet/AD site, there are no users resident in the second site.  Because of this, I'm thinking that I should use the numbers for a non-site resilient scenario, with two servers in each location across a single cross-subnet DAG.  Can anyone shed light on the different resource requirements here?  Thanks!

  44. Bruce JDC says:

    The totDBVolSpaceDAG value don't seem to take in account multi database per volume. there a IF that refer to VolArchitectyre<>"2 Volumes / Backup Set", however the VolArchitecture is set to "Multiple DBs / Volume"

  45. Bruce JDC says:

    Precision : we are in the scenario : NumDBCopies = 4, no log isolation and jbod evalution, the calculator show 2 DB / volume, but the calculator don't take that in account and multiply the number of volume per the number of database, doubling the total space req.

  46. Tim...M says:

    Thank you very much for this, an excellent guide to prep for hardware.  However, there is no mention of sizing for Public Folders.  In our production environment, we have almost a 1:1 ratio of PF's to users…in considering the migration from 2010 PF db to 2013 mailbox, should I account for these mailboxes as users – i.e., consider adding another 'Tier' of user class mailbox to this calculator, with calculated size and send/rcv per PF?  Thanks for any help on this!

  47. SteveT says:

    The calculator shows I need 24GB worth of RAM for the mailbox server no matter what I put in for the values.  Is this correct?

  48. Robert says:

    I don't understand why there's a 2 volumes per backup set (and/or the 2 volumes per database) Volume architecture.. can you tell me why it's telling me I need to have double the storage?  I'm not doing DAG's or anything else along those lines.  It seems to be related to backups maybe?

Comments are closed.