The BsdUnix solution to the problem, normally addressed in Linux by a JournalingFileSystem, of unexpected shutdowns sometimes leaving file system metadata in an inconsistent state.
Design and implementation: http://www.usenix.org/publications/library/proceedings/usenix99/full_papers/mckusick/mckusick.pdf
Comparison with journaling: http://www.usenix.org/publications/library/proceedings/usenix2000/general/full_papers/seltzer/seltzer_html/index.html