A word on Cluster Groups

Many clients are on Exchange 2003 or 2007 and will need to deal with Cluster Groups in Microsoft Cluster Services (MSCS) or Failover Clustering Services (FCS) including Cluster Continuous Replication (CCR).  So, it is important to understand one very critical restriction of Exchange Clustering that I’ve seen several clients trip over.

When installing a Microsoft Cluster of most flavors, you will configure Groups, which are logical units used to contain Resources like IP Addresses, Network Names, Disks and Services.  By default, a Cluster Group will be created that contains the name, IP address and Quorum Disk for the cluster itself.  It may also contain a networked Distributed Transaction Coordinator (DTC) resource for the cluster as a whole.  It is very tempting to place all other resources in this group, but you should avoid doing that at all costs for 2 significant reasons:

1 – It’s not supported by Microsoft.  For proof, I refer you to This TechNET article.  There is a long explanation of many thing having to do with configuring an Exchange Cluster, but here’s the specific info I’m referring to:

“It is an Exchange best practice to install the MSDTC resource into the default cluster group. However, the MSDTC resource is the only resource supported in the default cluster group. Exchange resources should not be added to the default cluster group, as that configuration is not supported.” [emphasis added]

TechNET and the Microsoft Sites have many other examples of this warning, and it is well documented by Microsoft and the Exchange Product Team.

2 – It makes life more difficult in day-to-day administration.  There may be instances where you want to perform operations on the Cluster Group without interrupting Exchange services for your organization.  You can normally accomplish this by moving the Cluster Group to a Cluster Node that isn’t hosting any Exchange Resource Groups, and perform your activities on that node.  If you have Exchange Resources in the Cluster Group, then this options disappears.  The same goes for many 3rd-Party products (see disclaimer at the end of the blog) which may not accept Exchange Resources that appear in the Cluster Group, as they must treat the Cluster Group and the Exchange Resource Group independently for administrative purposes.

So, as tempting as it is, avoid installing Exchange Resources into the Cluster Group at all costs.  If you already have put Exchange Resources into the Cluster Group, and you don’t plan on upgrading just yet, then seriously consider migrating to a supported cluster configuration when time permits.  Issues that arise from unsupported configuration and limited administration tend to hit without warning, and at the worst possible time.  Taking time to move to a supported platform will keep your organization in the safe zone, and make life a lot easier for you over time.