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Date: Sun, 4 Jan 2009 17:06:34 -0500
From: Theodore Tso <tytso@mit.edu>
To: Rob Landley <rob@landley.net>
Cc: Pavel Machek <pavel@suse.cz>, kernel list <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@osdl.org>, mtk.manpages@gmail.com,
       rdunlap@xenotime.net, linux-doc@vger.kernel.org
Subject: Re: document ext3 requirements
Message-ID: <20090104220634.GD22958@mit.edu>
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References: <20090103123813.GA1512@ucw.cz> <200901041349.49906.rob@landley.net>
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On Sun, Jan 04, 2009 at 01:49:49PM -0600, Rob Landley wrote:
> 
> Want to document the granularity issues with flash, while you're at it?
> 
> 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, ext3 won't notice that data in the 
> "sectors" _after_ the one your were trying to write to got trashed.

True enough, although the newer SSD's will have this problem addressed
(although at least initially, they are **far** more costly than the
el-cheapo 32GB SD cards you can find at the checkout counter at Fry's
alongside battery-powered shavers and trashy ipod speakers).

I will stress again, that most of this doesn't belong in
Documentation/filesystems/ext3.txt, as most of this is *not*
ext3-specific.

						- Ted
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