Exchange 2013 Sizing — Tips and Tricks Part 2

In our previous episode, we discussed the Exchange Server Role Requirements Calculator, and provided some tips on setting it up to do your Exchange 2013 sizing.

Let’s continue the discussion with discussing what drives Exchange server resource requirements.

Activity Levels Drive the Gear Train…

Key inputs for an Exchange 2013 sizing include the quantities of mailbox data the system will store, the amount of daily message traffic it will transact, and the types of clients that will be interacting with it.

Start with exporting the sizes of all of your databases and mailboxes, using the get-mailboxdatabase and get-mailboxstatistics commands in the Exchange 2010 Management Shell:

Get-MailboxDatabase -Status | select ServerName,Name,DatabaseSize,AvailableNewMailboxSpace | Export-CSV c:\DBSizes.csv
Get-MailboxStatistics -server "server" | Select DisplayName, Database, ItemCount, TotalItemSize | Sort-Object TotalItemSize -Descending  | Export-CSV C:\MBSizes.csv

Determining the amounts of daily send/receive activity is a bit more involved.  This script queries all of the hub/transport servers, downloads their message tracking logs, and calculates a wealth of statistics on a per-user basis for the previous day of mail routing activity.  Analyze the data and determine the number of received and unique messages sent per user.

The number of mobile device clients also affects system performance requirements.  Per slide 29 of Boris Lokhvitsky’s Ignite presentation, the “penalty factor” of some mobile device management solutions can be over 2x the cost of a normal ActiveSync device.

A System of Tiers…

When analyzing the mailbox sizing data, it helps to organize your data into “tiers” of users.  Indeed, the sizing calculator almost requires it.

Sort your listing of all mailboxes by size and look to see what the larger than average and smaller than average mailbox sizes are.  If your organization is similar to the many other I’ve worked with, there will be a mix of fewer larger mailboxes, a number of mailboxes that lie near the average, and perhaps a larger amount of mailboxes that are smaller than average but make up the largest number of mailboxes.

You could spend a large amount of time trying to classify your mailbox population into a tier classification, but overall we’ve had good success keeping the mailbox tiers relatively simple:

  1. > 10 GB
  2. 1-10 GB
  3. 100 MB – 1 GB
  4. < 100 MB

Your mileage may vary.  For example several legal environments that I’ve worked in have a much larger population of large size mailboxes, or organizations that have tightly controlled mailbox size may have a more uniform set of mailbox sizes.

Let’s proceed down the Input page, and review the settings for the Mailbox Configuration section.

Garbage In…?

After determining your mailbox tiers, determine the key inputs for them, namely:

  1. Total number of mailboxes
  2. Anticpated user growth
  3. Initial mailbox size (usually the average of all the mailboxes in the tier)
  4. Maximum mailbox size
  5. Average message size
  6. % of users running ActiveSync clients along with their regular Outlook or WebApp clients.


There are additional inputs to be configured on the Input tab of the sizing calculator, the remaining key one for our purposes today is the Backup Configuration section:


Enter your backup method, frequency, and number of days of backup failure tolerance.  These settings directly influence the sizing of the transaction log volumes.  While no amount of Exchange backup failure is “ok”, issues do sometimes occur, and it’s good practice to have enough transaction log space to allow time for troubleshooting without having to take drastic measure to keep the databases online.

In the next part, we’ll review the server and storage requirements generated by the calculator.

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

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