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Date: Fri, 24 Aug 2007 03:57:16 +1000 (EST)
From: Ian Smith <smithi@nimnet.asn.au>
To: CyberLeo Kitsana <cyberleo@cyberleo.net>
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Cc: Chris <chrcoluk@gmail.com>, freebsd-questions@freebsd.org,
	Bill Moran <wmoran@potentialtech.com>
Subject: Re: fsck strangeness
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On Thu, 23 Aug 2007, CyberLeo Kitsana wrote:
 > Ian Smith wrote:
 > > My knowledge of this is thin, despite reading McKusick's paper through
 > > several times, but we're told that background fsck runs on a snapshot of
 > > the fs concerned.  How any bg fsck corrections are woven back into the
 > > live fs later is still a mystery to me, but that's because I still have
 > > an only barely superficial understanding of how snapshots work ..
 > 
 > Background FSCK only repairs a small subset of filesystem
 > incosistencies. Specifically, those inconsistencies that softupdates
 > allows to occur, such as data blocks allocated out of the bitmap, but
 > not actually assigned to any inode. Background FSCK only needs to find
 > these (by looking at a fully consistent and unchanging snapshot of the
 > filesystem) and deallocate them in the live filesystem, a simple
 > operation given that it's guaranteed nothing will be using a block that
 > is both marked used and not assigned to anything.

Thanks for that nutshell, CL.  Sometimes little bits help the most <&^}=