"Native" journaling file systems?

Martin Cracauer cracauer at cons.org
Mon Dec 19 22:15:53 PST 2005

David Xu wrote on Tue, Dec 20, 2005 at 08:07:46AM +0800: 
> Matthias Andree wrote:
> >What has become of lfs by the way?
> >
> I am curious why nobody picks up the BSD lfs ? the UFS background fsck
> sucks us too bad, sigh.

If I am not mistaken, LFS was a pure log-structured filesystem, not a
normal filesystem with an added log.  That means it puts all the data
in addition to metadata into the log, and the log is all there is.

These filesystems are very difficult to make perform well if the exact
usage pattern is unkown.  In particular, garbage collection and the
compacting of the log is a fundamental problem.  Frequent deletions
are an obvious example.  I also think LFS did not have the capability
to overwrite existing blocks in existing files with new data, so
updates would lead to "shadowed" blocks at the end of the log,
potentially leaving a single file spattered all over the log and
making gargabe collection of deleted files in between a nightmare.

These filesystem can be excellent when you know what your usage
patterns are, or when you have a different API than the Unix API.
Immutable files in the API come to mind, they help these filesystems a
lot.  Won't help us run GNOME and mysql, though :-)

Martin Cracauer <cracauer at cons.org>   http://www.cons.org/cracauer/
FreeBSD - where you want to go, today.      http://www.freebsd.org/

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