Sidetracked: why gjournal over soft-updates (Was: Re: UFS2
Journaling implementation detail)
fbsd.questions at rachie.is-a-geek.net
Sat Apr 19 18:05:11 UTC 2008
On Friday 18 April 2008 17:40:04 Ivan Voras wrote:
> > 5. "Some UFS implementations avoid journaling and
> > instead implement soft updates: they order their
> > writes in such a way that the on-disk file system is
> > never inconsistent, or that the only inconsistency
> > that can be created in the event of a crash is a
> > storage leak. To recover from these leaks, the free
> > space map is reconciled against a full walk of the
> > file system at next mount." -
> > (http://en.wikipedia.org/wiki/Journaling_file_system)
> > So the disadvantage of Soft Update is it is necessary
> > to run fsck after reboot in event of a crash or power
> > failure?
> Yes. The advantage is that practically, the data is as safe as with
I've been following this with interest, however it's still not clear to me,
why I'd want a journaling filesystem, because:
1) If you have soft-updates the data is as safe as with journal
2) If you have soft-updates fsck will run in the background
3) Soft-updates don't require diskspace.
So...other then "journaling filesystems are cool", what's the real advantage?
Problem with today's modular software: they start with the modules
and never get to the software part.
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