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Date: Sun, 29 Oct 2000 20:46:38 -0800
From: "Crist J . Clark" <cjclark@reflexnet.net>
To: Arun Sharma <adsharma@sharmas.dhs.org>
Cc: freebsd-questions@FreeBSD.ORG
Subject: Re: softupdates and (avoiding) fsck
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Reply-To: cjclark@alum.mit.edu
References: <20001029183443.A27388@sharmas.dhs.org> <20001029190021.Z75251@149.211.6.64.reflexcom.com> <20001029191544.A27575@sharmas.dhs.org>
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On Sun, Oct 29, 2000 at 07:15:44PM -0800, Arun Sharma wrote:
> On Sun, Oct 29, 2000 at 07:00:21PM -0800, Crist J . Clark wrote:
> > There is no way around fsck'ing when the system is brought down
> > hard. (Not absolutely true, but you dowanna mount an unclean FS.)
> > Soft updates does _NOT_ guarantee that you will come out of such a
> > nasty thing without damage. It does make it much less likely,
> > however. Carefully read,
> > 
> >   /usr/src/sys/ufs/ffs/README
> > 
> > For more information on what soft updates really does.
> 
> That file doesn't exist in -current anymore. But I found some other
> file, which pointed me to:
> 
> http://www.mckusick.com/softdep/
> 
> which says:
> 
> > By ensuring that the only inconsistencies are unclaimed blocks or
> > inodes, soft updates can eliminate the need to run a filesystem check
> > program after every system crash. Instead, the system is brought up
> > immediately. When it is convenient, a snapshot is taken and a background
> > task can be run on on that snapshot to reclaim any lost blocks and
> > inodes. The use of a snapshot allows normal filesystem activity to
> > continue concurrently.

Good you found the paper. Section 6 deals with the issue. Also, have a
look at the fsck(8) source to see how it handles checking softupdate
filesystems. 
-- 
Crist J. Clark                           cjclark@alum.mit.edu


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