Exchange 2013 Sizing Cheat Sheet (Part 2)

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If you would like to read the first part in this article series please go to Exchange 2013 Sizing Cheat Sheet (Part 1).

CAS Role

The CAS role has changed again with this Exchange version, now it’s mostly a stateless proxy. CAS has also minimum hardware requirements, making multi-role deployment more attractive.


  • 2013 CAS requires 25% of Mailbox active-user mcycles (1:4 ratio)


  • 4GB minimum

Per-Server CAS Memory = 2GB + 2GB per physical processor core


  • There are no special needs regarding the disk subsystem


  • Gbit recommended


There is actually a recommendation to use a multi-role approach when designing an Exchange 2013 infrastructure. When gathering the CAS and Mailbox roles on the same server, memory and CPU have to be adjusted.


  1. Use the calculation from the Mailbox role
  2. Calculate the additional memory needs using the following formula:



Use this table instead of the one provided in the Mailbox role section:

Messages sent or received per mailbox per day Mcycles per User, Active DB Copy or Standalone (Multi-Role)
50 2.66
100 5.31
150 7.97
200 10.63
250 13.28
300 15.94
350 18.59
400 21.25
450 23.91
500 26.56

Table 1

Edge Role

The “new” Edge role was introduced with Service Pack 1 for Exchange 2013 and it’s basically a secure transport server to be placed in a perimeter network.


With A/V and A/S

Without A/V and A/S

Recommended processor cores / server



Edge Cores: mailbox   server cores ratio



Table 2


  • 4GB min
  • 1GB/core


  • Size storage capacity for queue requirements
  • Use the following calculation to size the Overall Transport DB Size:

Overall Daily Messages Traffic = number of users x message profile

Overall Transport DB Size = average message size x overall daily message traffic x (1 + (percentage of messages queued x maximum queue days) + Safety Net hold days) x 2 copies for high availability

In our example:

Overall Transport DB Size = 75KB x (5,000 users x 200 messages/day) x (1 + (50% x 2 maximum queue days) + 2 Safety Net hold days) x 2 copies = 429GB


  • Gbit recommended


Since virtualization is becoming popular in Exchange deployments, here are a few guidelines and recommendations:

  • Size for physical resources, add ~12% CPU overhead for hypervisor
  • Don’t oversubscribe resources
    • Disable dynamic memory
  • Host-based failover clustering and migration technologies are supported, but must result in cold boot or use technology similar to Hyper-V Live Migration for online migrations.
  • Snapshots are NOT supported.
  • Maximum of 2:1 virtual to physical CPU ratio, 1:1 recommended.
  • Must use block level storage.
  • VHDs must be fixed size.
  • Exchange data should be placed on storage that is separate from the storage hosting guest VMs.
  • Important technical documentation:

Validating the Solution

Before putting your newly sized servers in production, maybe you want to spend some time validating the deployed configuration. There are some tools from Microsoft that can help you with that task:

  1. Microsoft Exchange Server Jetstress 2013 – Jetstress simulates the Exchange database and log file loads produced by a specific number of users, thus allowing you to verify the performance and stability of your disk subsystem before putting your server into a production environment.
  2. Exchange Load Generator 2013 – Use Microsoft Exchange Load Generator 2013 (LoadGen) as a simulation tool to measure the impact of MAPI, OWA, ActiveSync, IMAP, POP and SMTP clients on Exchange 2013 servers. LoadGen allows you to test how a server running Exchange 2013 responds to e-mail loads. To simulate the delivery of these messaging requests, you run LoadGen tests on client computers. These tests send multiple messaging requests to the Exchange server, thereby causing a mail load. LoadGen is a useful tool for administrators who are sizing servers and validating a deployment plan. Specifically, LoadGen helps you determine if each of your servers can handle the load.
  3. Performance Monitor – Part of the Operating System, PerfMon uses the Exchange performance objects to retrieve counter information, provides information that allows you to gauge the health of your messaging solution.
  4. Managed Availability – Check for performance events related with performance checks made by the probes.

Third-Party Tools and Guidelines

Nowadays, most major hardware vendors have tools that facilitate the sizing process of the whole messaging infrastructure. Below you can find some of these tools from 2 of those hardware vendors (descriptions taken from the vendors’ website).

  • HP Sizer for Microsoft Exchange Server 2013 – Microsoft® Exchange Server 2013 is a complex application that requires thorough knowledge of deployment strategies, interdependencies, and server and storage performance goals. HP has developed the HP Sizer for Microsoft Exchange to assist customers with proper server and storage sizing and configuration for their Exchange deployments. The algorithms developed and implemented in this tool are based upon extensive knowledge of both Exchange and the hardware required to run it: CPU, memory, and storage subsystems. This tool is free to download and use, and is designed to allow very quick ‘what if’ modeling of various configurations and design choices. Once this Sizer is installed, updates can be downloaded automatically to the underlying software engines that are necessary to provide support for new HP server and storage product information details.This newest HP Sizer for Microsoft Exchange Server 2013 provides support for multiple site deployments, varied client profiles, combining or separating server roles, and Database Availability Group (DAG) high availability options. HP Server choices include tower, rack mounted (DL or SL), and HP BladeSystem server platforms. HP storage options include server-based storage, direct attached (DAS), shared DAS or storage area network (SAN) solutions. Based on your input, the tool provides a suggested bill of materials along with a deployment overview of the Exchange server roles and detailed storage configurations, including RAID, disk volumes and database copy layout.
  • Microsoft Exchange 2013 on VMware Design and Sizing Guide – Microsoft Exchange can be complex to deploy, and there are many design decisions to make to build a solid solution. Running Microsoft Exchange Server 2013 on VMware® vSphere® can positively impact design, deployment, availability, and operations, but what does such a solution look like?This document explores sample architecture designs that illustrate Exchange 2013 environments running on vSphere. The focus of this architecture is to provide a high-level overview of the solution components, with diagrams to help illustrate key concepts.


This article is a brief introduction to the sizing process of an Exchange 2013 infrastructure. For a real world deployment of Exchange 2013, I strongly recommend the use of the Exchange 2013 Server Role Requirements Calculator, as well as solid knowledge on the subject of the various components of such a messaging infrastructure. For more information, use the links provided below.

Related Links

If you would like to be notified of when Rui Silva releases the next part in this article series please sign up to our Real Time Article Update newsletter.

If you would like to read the first part in this article series please go to Exchange 2013 Sizing Cheat Sheet (Part 1).

About The Author

1 thought on “Exchange 2013 Sizing Cheat Sheet (Part 2)”

  1. “Overall Transport DB Size = 75KB x (5,000 users x 200 messages/day) x (1 + (50% x 2 maximum queue days) + 2 Safety Net hold days) x 2 copies = 429GB”

    Please can you confirm if this calculation is correct? I tried it and get 572GB?:

    75 x 100000 x 4 x 2 = 600000000KB = 572GB

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