The Exchange Server 2013 architecture consists of three roles: the Mailbox and Client Access (CAS) roles are deployed...
internally, and the Edge Transport role is deployed in the perimeter network.
Moving from an Exchange 2013 single-server to a multiserver deployment for high availability does not require replacing any deployed servers. Since you have a single server deployed for Exchange, the Mailbox and CAS roles exist on the same server. The easiest way to get to a highly available multiserver architecture is to add another server with both roles installed.
You can then set up a database availability group since DAG members can have both roles installed. After you make both servers DAG members, continue to scale up to 15 or fewer member servers deployed in the single DAG.
Before you start, answer these questions about your current Exchange 2013 single-server setup:
- Which operating system is installed on the server?
- Which Exchange edition is installed on the servers?
- Are there multiple domains in the Active Directory forest?
- Which load balancing tool will you use for client access?
DAGs require that the underlying OS supports failover clustering and all DAG member servers must run the same OS version and edition.
DNS Round Robin and HLB can be used with a combined role server deployment; however, Windows NLB and Exchange DAGs are mutually exclusive technologies and cannot be deployed on the same server. If you want to use Windows NLB, deploy separate servers for CAS and Mailbox roles. Deploy combined roles and use a HLB solution.
The Exchange 2013 Standard Edition is supported as a DAG member; however, it is limited to five mounted database copies (active or passive) per server. Scalability is limited if you plan to deploy numerous databases. On the other hand, the Exchange 2013 Enterprise Edition supports up to 50 mounted databases per member.
All DAG members must share the same Active Directory domain. If you have more than one domain, join the new Exchange 2013 server(s) into the same domain as the existing single server. DAG members can reside in different sites, but only if you plan the multiserver architecture so that Exchange maintains a quorum if the network between sites goes down.
About the author:
Richard Luckett is a consultant and instructor specializing in messaging and unified communications. He's been a certified professional with Microsoft since 1996 and has 20 years of experience in the public and private sectors. Luckett is a Microsoft Certified Trainer with more than 15 years of training experience with the Microsoft product line and received the Exchange MVP award in 2006, 2007 and 2008. He's also an expert in deploying and integrating Exchange Server and Lync Server. He leads the Microsoft training and consulting practice at LITSG.
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