linux-kernel - Re: Implementing NVMHCI...

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Message-ID: <20090430225153.GA14784@logfs.org>
Date:	Fri, 1 May 2009 00:51:53 +0200
From:	Jörn Engel <joern@...fs.org>
To:	Artem Bityutskiy <dedekind@...radead.org>
Cc:	Jared Hulbert <jaredeh@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Szabolcs Szakacsits <szaka@...s-3g.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Grant Grundler <grundler@...gle.com>,
	Linux IDE mailing list <linux-ide@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Arjan van de Ven <arjan@...radead.org>,
	David Woodhouse <dwmw2@...radead.org>
Subject: Re: Implementing NVMHCI...

On Wed, 15 April 2009 09:37:50 +0300, Artem Bityutskiy wrote:
> 
> I briefly glanced at the doc, and it does not look like this is an
> interface to expose raw NAND. E.g., I could not find "erase" operation.
> I could not find information about bad eraseblocks.
> 
> It looks like it is not about raw NANDs. May be about "managed" NANDs.

I'm not sure whether your distinction is exactly valid anymore.  "raw
NAND" used to mean two things.  1) A single chip of silicon without
additional hardware.  2) NAND without FTL.

Traditionally the FTL was implemented either in software or in a
constroller chip.  So you could not get "cooked" flash as in FTL without
"cooked" flash as in extra hardware.  Today you can, which makes "raw
NAND" a less useful term.

And I'm not sure what to think about flash chips with the (likely
crappy) FTL inside either.  Not having to deal with bad blocks anymore
is a bliss.  Not having to deal with wear leveling anymore is a lie.
Not knowing whether errors occurred and whether uncorrected data was
left on the device or replaced with corrected data is a pain.

But like it or not, the market seems to be moving in that direction.
Which means we will have "block devices" that have all the interfaces of
disks and behave much like flash - modulo the crap FTL.

Jörn

-- 
Courage is not the absence of fear, but rather the judgement that
something else is more important than fear.
-- Ambrose Redmoon
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