CCR clustering is still clustering, and so is DAG

As more and more of my readers move to Exchange 2007 and 2010 from Exchange 2003 and earlier versions, I hear a lot about how using the new High Availability tools will finally free them from the yolk of clustering in Windows.  While both CCR and DAG are definite improvements over traditional shared-disk clustering, neither is a departure from clustering entirely.

We’ll be talking about the new HA stuff in Exchange 2010 (along with much more of course) in the webinar Double-Take Software and Microsoft are presenting tomorrow.  I’m the speaker for Double-Take, and Patrick Foley from Microsoft is going to be doing their portion. It’s September 9th at 11am, and you can still register for free by clicking here.

In the meantime, it is important to realize that both CCR (Continuous Cluster Replication) and DAG (Database Availability Groups) are offshoots of Windows Failover Clustering (WFC).  They both change the way WFC works, and by quite a lot, so you may never touch the underlying cluster technology, but it is still there.

CCR – as its name implies – works by allowing you to create a cluster during the installation of Exchange 2007.  This one is a bit easier to see as part of WFC, as you have to create a Failover Cluster first – specifically a Distributed Majority-Node File Share Witness Failover Cluster.  After that, when you install Exchange Server you can specify which server(s) will be the Active node(s) and which will be passive.  This creates the clustered Exchange resources for you, making the overall process of setting up clustering for Exchange a lot easier.  As this one has Cluster in the name, it’s easier to see the WFC roots.

DAG will permit you to create the cluster itself from Exchange 2010 command sets, eliminating the need to pre-create the Failover Cluster prior to getting the Exchange installation rolling.  While this makes the process even easier than in 2007, it still requires that you have two or more servers capable of running Distributed Failover Clustering.  This means that not every version of Windows 2008 is going to be suitable for DAG, but also means that – under the hood – you still need to know how Distributed Failover Clustering works to properly manage the DAG systems.

In both cases, the required level of understanding of clustering is greatly diminished from what was needed in Exchange 2003 and earlier versions.  Most of the guts of the cluster are controlled by Exchange itself, which is a double-edged sword.  On one side you have the fact that folks who don’t have a lot of cluster know-how can now set up HA solutions for Exchange.  On the other side, people who don’t have a lot of cluster know-how are facing troubleshooting clustered Exchange solutions they may not have realized were there.

Both solutions work great for Exchange.  While they don’t eliminate the need for 3rd-party products to help with overall HA (and I’m biased on this one, see disclaimer below), they do make mailbox server protection much more complete.  Just remember that you’re still running on a cluster, and arm yourself with the knowledge needed to keep it running smoothly.