Sidetracked: why gjournal over soft-updates (Was: Re: UFS2 Journaling implementation detail)

Mel fbsd.questions at
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." -
> >  (
> >
> >  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
> journalling.

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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