Time to pay the bills! Exchange 2003 and GeoCluster.

Exchange 2007 introduced the idea of Cluster Continuous Replication (CCR) to the world, allowing you to extend an Exchange Cluster between sites (especially on Server 2008) and to create more than one copy of the mailbox data. Exchange 2010 will introduce Database Availability Groups (DAG), further pushing the technology to provide up to 16 total copies of the mailbox data in any number of locations. Both of these technologies are stellar in their own right, but leave those who are still running Exchange 2003 solidly in the dust. Granted, Exchange 2003 is nearing end-of-life, but with a large portion of the market still running on it (at the very least until the upgrades are done), many folks need solutions.

As I work for Double-Take Software, of course I’m happy to advocate our cluster-extending technology to help alleviate the situation on earlier versions of Exchange Server. This is both because they pay me to vocally advocate it (the FCC may be watching) and because it works remarkably well. More so for the latter reason.

GeoCluster (which was once a stand-alone product but is now a feature set of Double-Take Availability), allows you to create a Microsoft Cluster using Microsoft Clustering Services (MSCS) on Server 2003, but to do so without creating a shared-disk configuration that could lead to a single-point-of-failure and will restrict you in terms of how far apart the nodes can physically be. The idea is simple, GeoCluster works under the hood of MSCS, replicating data on each disk resource from the owning node to all potential owning nodes in the cluster. So Exchange sees a traditional cluster, but in reality the disks are replicated, creating multiple copies of the data based on the active node for each disk.

Since GeoCluster can support any valid cluster configuration, you can freely create clusters that span more than 2 nodes, or even more than one physical site. Keep in mind, however, that you’ll still be limited by single-subnet restrictions in Server 2003’s MSCS implementation. The good news is that moving resources from node to node works exactly the same was as it would in a shared-disk cluster, and therefore automatic failover and on-command moves are all possible.

If you lose a node, GeoCluster lets the MSCS engine arbitrate who should take over, then begins replicating data from that new owner to all the other, surviving, potential owners. Once you repair or replace the original node, the system will sync up the volumes and be ready to allow you to move the resources back to the original node if you want to. This replication is all done with the Double-Take Replication Engine, which allows GeoCluster to have the same level of write-order integrity and data reliability as any other Double-Take connection.

So, until you’re ready to make the jump to Exchange 2007 and beyond, or if you cannot take advantage of CCR for whatever reason, have a look at the GeoCluster solution. It is a cost effective and reliable way to make MSCS even more flexible and reliable, and does so without making Exchange work differently than it was designed to function.

Don’t believe me?  Check out this TechNET blog post about what the MSFT Virtualization Team does with partners like DBTK.  We help them with clustering solutions for Hyper-V, and can help you with that and much more.

Tomorrow, back to my usual, non-vendor-specific stuff =)