linux-kernel - Re: [ANNOUNCE] util-linux-ng v2.17 (stable)

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Message-ID: <4B4BB397.5090500@zytor.com>
Date:	Mon, 11 Jan 2010 15:26:15 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Pavel Machek <pavel@....cz>
CC:	Karel Zak <kzak@...hat.com>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, util-linux-ng@...r.kernel.org
Subject: Re: [ANNOUNCE] util-linux-ng v2.17 (stable)

On 01/11/2010 12:17 PM, Pavel Machek wrote:
>>
>> Uhm, that's just plain wrong.
>>
>> It doesn't matter if there is a "special mapping layer" -- if you're
>> crossing multiple erase blocks you're still having more churn in
>> your flash translation layer, with more wear on the device, and
>> lower performance than if you didn't.
> 
> Eraseblocks really should not matter. It is not as if each logical
> sector belongs to one eraseblock....
> 
> (OTOH, maybe the eraseblock *groups* that are basis for wear-leveling
> do, or maybe firmware is doing something really really strange.)
> 								Pavel

Maybe they "should not" matter, but they *do* matter.  In most existing
FTLs, each logical sector *does* belong to one erase block, although
which particular erase block that is of course moves around.  However,
the invariant that matters though -- and the reason alignment matters --
is that for most FTLs, the *offset* of any particular logical sector
within the erase block it currently belongs to is invariant, i.e. the
FTL operates on physical sectors which are the same size as the erase
blocks.

	-hpa
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