Are you using the most recent DragonFly code from CVS? Matthew Dillon warns that the new red/black tree work may be causing file system problems. If this worries you, you should be running with a less dangerous tag in your cvsup file. (See his post for details.)
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It’s not the red/black trees work.
Some weird bug in CVS, just the entire sequence of problems led me to believe a subtle fs corruption.