title: Why is MSDTC not supported when using SQL Server Mirroring & Automatic Failover?
body: <p>I have an application that I would like to have support SQL Server Mirroring.  However, the architecture is currently such that multiple WCF services and DB connections will be enlisted in a single MSDTC transactions, and Microsoft states that MSDTC is not supported when using Mirroring.</p>
  
  <p><a href="http://support.microsoft.com/kb/926150" rel="noreferrer">Their explanation</a> is not terribly informative:</p>
  
  <blockquote>
    <p>A similar scenario can occur when you use database mirroring with MS DTC transactions. For example, the new principal server contacts the MS DTC after a failover. However, the MS DTC has no knowledge of the new principal server. Therefore, the MS DTC stops any transactions that are in the "preparing to commit" phase, even though the transactions are considered committed in other databases.</p>
  </blockquote>
  
  <p>What I am having a problem understanding is the last sentence.  How is this any different than if the DB server was not mirrored, and just died at that same point in time?  Can someone explain that to me?  I need to be able to explain this to others in my organization (as well as customers), but I don't understand why MSDTC can properly rollback/compensate in one scenario, but it cannot if one of the participants is a mirrored SQL server (in Full Safety mode).</p>