Planning Active Directory for Exchange 2013: Global Catalog and Mailbox Server Placement

This post will describe in quick summary some of the ideals for Active Directory with Exchange 2013.  I will not go into detail about the different server roles but will describe some best practices regarding the placement of Global Catalog and the Mailbox Server.

Global Catalog Server Placement

At this point you probably already have a domain and are thinking of optimizing it for Exchange or already have an Exchange environment in your domain and would like to maximize Exchange performance.  

You should know that Exchange 2013 places heavy emphasis on the use of the Global Catalog in Active Directory.  For this reason we need to be sure that our domain has Sites appropriately configured and that replication has been tailored to your particular environment.  

Because of the intertwining of Active Directory and Exchange, it is recommended to have at least one Global Catalog in every site and Microsoft recommends two GC's for every site.  This is useful because the GC and the Site Links are both queried any time a piece of mail is routed through your domain.  You will want to do your best efforts to reduce the time to find a mailbox in your domain by configuring Sites and Site Links appropriately for replication and make sure you have at least one GC in each site.

Mailbox Server Placement

In Exchange 2013 there is a much heavier use of the Mailbox role to process mail.  The CAS role has become a simple proxy server to find what mailbox database a mailbox sits on, and to find the next hop for the mail to travel.  This leaves much of the processing between the client and the mailbox database on the Mailbox server.

Because of this transition it is highly recommended to place a Mailbox server as close to the client as possible.  You may even find yourself with sites without the need of a CAS server.  

We will setup one of our sites in the lab with just a mailbox server so you can see how this will look.  

Here is a very simple diagram on how this might look:

In this diagram we have users at every site but Branch Office 1 is a much smaller office.  Because they do not have IT staff on site, we will only place a single DC and a single Mailbox server.  This will provide the best user experience with the least amount of overhead.

NOTE: RODCs are not recommended as a solution for Exchange servers.  If you have a site will mail users and an RODC, place the Mailbox server and their mailbox database at the closest site with a full blown DC.

This concludes Planning Active Directory for Exchange 2013: Global Catalog and Mailbox Server Placement.

I hope this was helpful and informative to you and I would appreciate any feedback you may have.