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Ned here again. I’m frequently asked to explain the DFSR conflict algorithm – i.e. what happens when files are created or modified on two servers before replication takes place. What we don’t document well is that there are actually three conflict algorithms and they all behave quite differently. I am breaking these out into scenarios for easier understanding.
(Note: updated 3/25/2011 with some newer behaviors)
Scenario 1: Brand new files in initial sync with different versions of the file on each server.
Result: salespitch.pptx from A (dated July 2009) will now exist on both servers. The October version will be conflicted on B and it will lose the conflict.
Explanation: When setting a server as Primary, it wins all conflicts no matter what. This is the so-called “Initial Sync conflict algorithm”.
Scenario 2: Existing files that have been replicated previously and are now being modified on two servers before replicating.
Result: The file I modified last (i.e. the newest file with the latest UTC time stamp) replicates from A to B. B loses the conflict and his older copy will be conflicted.
Explanation: This is the classic “last writer wins conflict algorithm” that is usually described for DFSR.
Scenario 3: New files that were created on both servers before replicating, but initial sync is not happening
Result (Windows Server 2003, Windows Server 2008, Windows Server 2008 R2 without KB2450944 installed): The old file on A is replicated to B, and B loses the conflict. Result (Windows Server 2003, Windows Server 2008, Windows Server 2008 R2 with KB2450944 installed): The new file on B is replicated to A, and A loses the conflict.
Explanation: This was the only time an older file would win and this was the so-called “New to DFSR file conflict algorithm”. The reasoning was that when it came to two files being created, the oldest one was likely the most important as it has been in use the longest. But this turned out to be too confusing and likely to cause other issues, so it was changed to match the more consistent "last writer wins" behavior in a hotfix later.
That’s all well and good. But how do I get my conflicted files back when the “wrong” one wins?
You have a few options here:
Hopefully this makes more sense now.
- Ned “the mediator” Pyle