Ever since I went to the Yukon Technical Preview back in Feb 2003, I have loved the idea of DB Mirroring.  With the anticipated release of SP1 for SQL Server 2005 right around the corner (we think), it is a good bet that DB Mirroring will be part of the package.  Last year, I was fortunate enough to be able to participate in leading discussions at the Get Ready for SQL Server 2005 Road Shows at a good number of cities.  My favorite session was on High Availability.  Since RTM, I have largely ignored DB Mirroring until a colleague of mine pointed out a discrepancy between BOL and the behavior found in the CTPs.  Last week, I was able to get this question answered by an inside source.  There has been a behavior change from the earlier CTPs to RTM in High Protection Mode for DB Mirroring.

High Protection Mode means "Synchronous" behavior without a Witness.  Another way to describe this is SAFETY=FULL without a witness.  As the case described in the earlier CTPs, if the Mirror Server fails, the Principal would stop processing since it could not guarantee that the transaction could be written in two places.  Now, in RTM, the Principal will keep processing if the Mirror fails.  Either behavior could be argued to be the desird behavior depending upon your point of view.  I just wanted to state it clearly for those of you who are interested in this feature but have not delved into the details yet.  There is no change in Behavior if the Principal fails.  If this happens, the DBA must force service manually to the Mirror server to make it the new Principal.