A sidenote to KludgeFS ... ChunkFS
This one is to good too leave it in the comments: Val Henson coauthored the ChunkFS paper, which states:
A few file systems, such as ZFS, have gone as far as checksumming and duplicating all file system metadata, which reduces the frequency of fsck but not the overall time.
The on-disk state is always valid. No more fsck, no need to replay a journal. We use a copy-on-write, transactional update system to correctly and safely update data on disk. There is no window where the on-disk state can be corrupted by a power cycle or system panic. This means that you are much less likely to lose data than on a file system that uses fsck or journal replay to repair on-disk data corruption after a crash. Yes, supposedly fsck-free file systems already exist - but then explain to me all the time I've spent waiting for fsck to finish on ext3 or logging UFS - and the resulting file system corruption.
Kudos to Chad for pointing me to this one …