Exchange Server 2010: Database Availability Group

Database Availability Groups are one of the best features to be added to Exchange 2010, according to Raphael Barini.

Now that Exchange 2010 has been officially released, I want to draw your attention to what I believe is one of the best features added to Exchange 2010.

There may be some people who will miss a few features of Exchange 2007 that were removed; however, DAG is a feature that many administrators have been requesting for years.

Exchange 2007 was launched with some great features, and introduced the LCR, CCR, SCC and SCR means of clustering Exchange servers.

LCR (Local Continuous Replication) was mainly used in small businesses who wanted to have a local copy of their Exchange database replicated to another disk on the same server:



SCC (Single Copy Cluster) is what I would call a traditional Exchange cluster, in which you use a shared storage to host the Exchange database.



CCR (Cluster Continuous Replication) was used to replicate Exchange database between two Exchange servers, allowing for hardware and storage redundancy, but it has one limitation—just one active and one passive node.



SCR (Standby Continuous Replication) was introduced in Exchange 2007 SP1 to provide the ability to replicate Exchange databases to a disaster recovery location.



The concept of a DAG and how it functions is more easily learned by someone who hasn’t worked with Exchange clusters in the past because it is simple and easy to use in comparison to any other earlier version of Exchange.

In Exchange 2007, an Exchange Server was installed as either an Active or Passive cluster node at the time setup.exe was run.

Depending on which version of Exchange you installed, you had to create an Exchange virtual server (EVS) which was changed to cluster mailbox server (CMS) in Exchange 2007. When a user connected to Outlook, the mailbox server name was a clustered resource which moved between any number of nodes on the Exchange cluster.

This allowed for no end user configuration changes; instead, all the resources moved between physical servers. An Exchange database was associated with the clustered resource and when you opened EMC/ESM the only Exchange server name that was shown was the clustered node (let’s call is CMSORG1.) That means database one would always belong to CMSORG1 even when this moved between physical machines.

Without further ado, here comes the DAG…

Now it’s time to forget everything that I mentioned previously about Exchange clustering. What has been removed?

1) No more EVS/CMS
2) Database is no longer associated to a Server but is an Org Level resource
3) There is no longer a requirement to choose Cluster or Non Cluster at installation. (An Exchange 2010 Server can move in and out of a DAG as needed)
4) The limitation of only hosting the mailbox role on a clustered Exchange server
5) Storage groups have been removed as well from Exchange

What still have the same requirements? 

Windows and Exchange Enterprise Edition is still required since DAG still uses pieces of Windows Failover Clustering.

What is new in Exchange 2010 DAG?

1) Other roles can be installed on the mailbox server when it is a member of a DAG
2) A database name must be unique in the Exchange Organization



DAG can also be extended in multiple Active Directory Sites.



We've put together a video that walks you through the installation of Exchange 2010 and then sets up DAG.

To view the video, please click this link, then click the full screen icon in the bottom right hand corner.
 
I hope you enjoy DAG as much as I do, and many thanks to Microsoft and the Exchange Team for this great new feature.