Date: Mon, 5 Jan 2009 10:38:17 +0100
From: Pavel Machek <pavel@suse.cz>
To: david@lang.hm
Cc: Rob Landley <rob@landley.net>, kernel list <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@osdl.org>, tytso@mit.edu, mtk.manpages@gmail.com,
       rdunlap@xenotime.net, linux-doc@vger.kernel.org
Subject: Re: document ext3 requirements
Message-ID: <20090105093817.GA27199@atrey.karlin.mff.cuni.cz>
References: <20090103123813.GA1512@ucw.cz> <200901041349.49906.rob@landley.net> <20090104225545.GF1913@elf.ucw.cz> <alpine.DEB.1.10.0901041615560.25545@asgard.lang.hm>
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> >Sector writes are atomic (ATOMIC-SECTORS)
> >~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >
> >Either whole sector is correctly written or nothing is written during
> >powerfail.
> >
> >       Unfortuantely, none of the cheap USB/SD flash cards I seen do
> >       behave like this, and are unsuitable for all linux filesystems
> >       I know.
> >
> >               An inherent problem with using flash as a normal block
> >               device is that the flash erase size is bigger than
> >               most filesystem sector sizes.  So when you request a
> >               write, it may erase and rewrite the next 64k, 128k, or
> >               even a couple megabytes on the really _big_ ones.
> >
> >               If you lose power in the middle of that, filesystem
> >               won't notice that data in the "sectors" _after_ the
> >               one your were trying to write to got trashed.
> 
> around, not after. the block you are reading could be in the middle or at 
> the end of an eraseblock.

Applied, thanks.

-- 
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