Thursday, September 08, 2005

Exchange clusters and the Microsoft Distributed Transaction Coordinator

This week there has been some discussions on one of the e-mail lists to which I describe about the proper placement of the MSDTC (Microsoft Distributed Transaction Coordinator) resource in an Exchange-only cluster. Over the past couple of years, I have seen recommendations that state that it should be in its own cluster resource group (with its own physical disk, IP address, and network name) versus putting the MSDTC resource in the Cluster group with the cluster quorum and the quorum drive. Even Microsoft's own guidance on this has been less than consistent.

First, a little background, while Exchange does not directly use the MSDTC in a cluster, it is required on a cluster during Exchange setup and service packs. Therefore, the MSDTC is really used less than 1% of the time in a cluster.

Thanks to this lively discussion, the Microsoft documentation (including the Exchange High Availability Guide and the Deployment Guide) as well as a few KB articles are going to be updated to reflect Microsoft's recommended Best Practices.

So, the best practice for the MSDTC is to put it in the default Cluster Group with the cluster name resource, cluster IP address, cluster quorum resource, and the cluster quorum drive. If you are concerned about a failure of the MSDTC causing a fail-over of the entire Cluster Group, on the Advanced property page of the MSDTC properties, clear the "Affect the Group" checkbox. I personally recommend this additional step.

Please note that this advice does not hold up in a cluster that supports SQL Server, as SQL Server makes more use of the MSDTC and thus it may be important that the MSDTC is in its own resource group and uses a dedicated disk drive.


At 1:54 PM, Blogger Devin L. Ganger said...

When we wrote the Solution Accelerator for Exchange Consolidation and Migration last year, we followed this practice as well. Just for fun, I include the relevant paragraphs from the Implementation Guide:

Once the basic cluster configuration was operational and the shared disk and network resources had been added and defined, the Contoso administrators created the Microsoft Distributed Transaction Coordinator (MSDTC) resource. While this resource is not required for day-to-day Exchange operation, it must be present for the Exchange setup process to be able to register the CDO Workflow Event Sink using COM+; this resource must also be present during the installation of Service Packs.

Microsoft Knowledge Base article 301600 (“How to configure Microsoft Distributed Transaction Coordinator on a Windows Server 2003 cluster”) provides a detailed description of the recommendations for installing the MSDTC resource. The Contoso administrators followed this advice, modified by the checklist in the Exchange Server 2003 Cluster Configuration Checklist on Microsoft TechNet, to configure the MSDTC resource within the default cluster group, set to not affect the failover state of the cluster group. This configuration provided the Contoso Exchange cluster with an effective compromise between economy and stability; if the MSDTC resource fails to another node, it will not cause the failover of the Exchange resources as well.


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