linux-kernel - Re: ATA 4 KiB sector issues.

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Message-ID: <20100309115017.GF18077@nb.net.home>
Date:	Tue, 9 Mar 2010 12:50:18 +0100
From:	Karel Zak <kzak@...hat.com>
To:	Michael Tokarev <mjt@....msk.ru>
Cc:	Mike Snitzer <snitzer@...hat.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Tejun Heo <tj@...nel.org>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Daniel Taylor <Daniel.Taylor@....com>,
	Jeff Garzik <jeff@...zik.org>, Mark Lord <kernel@...savvy.com>,
	tytso@....edu, "H. Peter Anvin" <hpa@...or.com>,
	hirofumi@...l.parknet.co.jp,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, irtiger@...il.com,
	Matthew Wilcox <matthew@....cx>, aschnell@...e.de,
	knikanth@...e.de, jdelvare@...e.de,
	Jim Meyering <jim@...ering.net>, Neil Brown <neilb@...e.de>
Subject: Re: ATA 4 KiB sector issues.

On Tue, Mar 09, 2010 at 01:16:01PM +0300, Michael Tokarev wrote:
> Karel Zak wrote:
> >  # mdadm --create /dev/md8 --level=5 --raid-devices=4 /dev/sdb{1,2,3,4}
> 
> That's 3-disk stripe size with default 64Kb chunk size, which makes
> 3x64=320KiB - the number to which everything should be aligned.
> 
> >  # fdisk -lcu /dev/md8
> > 
> >  Disk /dev/md8: 1572 MB, 1572667392 bytes
> >  2 heads, 4 sectors/track, 383952 cylinders, total 3071616 sectors
> >  Units = sectors of 1 * 512 = 512 bytes
> >  Sector size (logical/physical): 512 bytes / 4096 bytes
> >  I/O size (minimum/optimal): 65536 bytes / 65536 bytes
> 
> And here we go: fdisk does not see the right number: nothing
> is dividable by 3.
> 
> []
> >  # cat /sys/block/md8/md8p{1,2}/alignment_offset
> >  0
> >  0
> 
> And that's where the issue is.  md does not {sup,re}port all
> this stuff yet.
> 
> This is what I'm talking about.

Note that I have 2.6.31.12-174.2.22.fc12.x86_64 kernel on my laptop.
It would be better for serious tests to use 2.6.33.

    Karel
 
-- 
 Karel Zak  <kzak@...hat.com>
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