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

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Message-ID: <20100309111523.GL28189@discord.disaster>
Date:	Tue, 9 Mar 2010 22:15:23 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Michael Tokarev <mjt@....msk.ru>
Cc:	Karel Zak <kzak@...hat.com>, 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:
> > I did almost all my tests with scsi_debug or MD RAID0 on scsi_debug.
> > It works as expected.
> 
> Actually, for raid0, the alignment is questionable.  Should it be a
> multiple of chunk size or whole stripe size?  I'm not sure, both ways
> has bad and good sides..  But if it is the latter, the same issues
> pops up again: do a 3-disk raid0 and you'll have to align to 3*2^N.

Yes, alignment is still needed, especially for filesystems that can
do stripe unit aligned allocation like XFS. If you don't align the
filesystem properly, all the data IO will be mis-aligned to the
underlying disks and stripe unit sized IO will hit multiple disks
rather than just one....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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