You may have read something about DFS replication in Server 2008. (DFS stands for Distributed File System or Distributed File Service.) Or perhaps you've been using this feature, which (among other capabilities) lets you create multiple redundant targets for file shares that you want to make available to network users. The DFS replication service (also known as DFS-R) is responsible for synchronizing updates to files that exist in more than one DFS target location. The version of DFS-R that comes with Server 2008 and Server 2003 R2 is dramatically better than earlier versions because the new version replicates only changes to affected files, not the entire files.
One of the questions that usually comes up is whether Windows has some way to automatically lock a file in a DFS target so that a simultaneous update to the same file in another target folder cannot occur. Alas, this capability is not part of DFS, even in Server 2008. What will happen is the “last write wins” and the earlier of the two simultaneous updates will get overwritten and lost.
The moral here is that DFS-R is not a distributed database system. If you expect frequent simultaneous updates of files in your DFS target folders, then DFS may not be the best tool to use to provide fault tolerance or performance benefits. Microsoft would likely suggest SharePoint for such scenarios, because it offers a check-out/check-in system.
Glenn Weadock is a longtime instructor for Global Knowledge and teaches Windows 7, Server 2008, and Active Directory. He has recently co-developed with Mark Wilkins two advanced Server 2008 classes in the Microsoft Official Curriculum. Glenn also consults through his Colorado-based company Independent Software, Inc. and is technical director of MarketCoach Investment Education Software LLC.
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