Double-Take Software

Last week we talked about how Double-Take Software products can help provide a well-rounded solution to Exchange 2007 Disaster Recovery (DR) and High Availability (HA) in single-server environments.  Now let’s take a look about larger environments that will split the core roles onto their own servers.  Core roles are the Mailbox Role (MB), Hub/Transport Role (HT), and Client Access Server Role (CAS). 

For multi-server environments, the built-in replication tools can be a great DR/HA plan when used in combination with 3^rd party tools.  For mid-tier and larger environments, the logical choice is a Continuous Cluster Replication (CCR) cluster setup.  This is a Microsoft Exchange Server 2007 technology that allows you to create and Exchange cluster without the need for a shared-disk infrastructure, as you would normally need for clustered applications.  There are, however, a few limitations to this type of configuration when it comes to DR.

First, as with all the forms of replication built into Exchange 2007, you’re going to be limited to one Store per Storage group.  While Exchange 2007 can support up to 50 Storage Groups per server, that could still lead to a lot of management overhead if you have a large number of users spread across a large number of Stores. 

Secondly, CCR clusters will require that you have all nodes and services on the same subnet, unless you are moving your servers onto the new Windows 2008 platform.  This could be a severe limitation if you want to be able to fail over across multiple sites.  You could use Standby Continuous Replication (SCR) to move the data out of the cluster and onto a server at another site, but then you will have to perform both manual failover through Database Portability, and handle failback via a move mailbox operation – not the easiest recovery solution.

Finally, clustering is only available for the Mailbox Role, all other servers must be located on non-clustered systems, which means CCR will not help you with those, even on Server 2008.

So here, as with more simple Exchange 2007 environments, you may want to look into 3^rd party tools for a more well-rounded DR/HA solution set.  Double-Take Software products can definitely help with that, by using the Double-Take Application Manager for the MB servers, and the Full Server Failover solution for the other roles.  These tools provide automated failover for all roles in the Exchange 2007 Server System, and provide a failback procedure that can help you get back to the original server – or a new one if necessary.

In any mid to enterprise-sized Exchange 2007 environment, the tool-set that now comes built-in to Exchange will allow you to accomplish many of your DR and HA goals.  Combining these tools with 3^rd party products like the Double-Take line will offer more complete protection, failback, and even assist with tougher DR projects like Edge Services and Unified Messaging.