linux-kernel - Re: Slow disks.

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Message-ID: <m3pqsnnklz.fsf@intrepid.localdomain>
Date:	Mon, 27 Dec 2010 19:20:24 +0100
From:	Krzysztof Halasa <khc@...waw.pl>
To:	Mark Knecht <markknecht@...il.com>
Cc:	Jeff Moyer <jmoyer@...hat.com>,
	Rogier Wolff <R.E.Wolff@...wizard.nl>,
	Greg Freemyer <greg.freemyer@...il.com>,
	Bruno Prémont <bonbons@...ux-vserver.org>,
	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org
Subject: Re: Slow disks.

Mark Knecht <markknecht@...il.com> writes:

> Even when I got that part worked out I found that the drives just
> didn't work well in a RAID. The mdadm list led me to believe that the
> root cause was the lack of TLER in the firmware. I don't know how to
> show that's true or not...

But TLER only matters when the drive can't read a sector. For a normal
drive which can easily read all its sectors (at least without retrying
for several seconds) TLER doesn't matter.

Alignment, sure. Personally I'd use whole disks (not partitions) for
RAID-5 and partition the resulting /dev/md* instead, taking into account
even longer "sector" size.

Or better, use RAID-1 (or RAID-10) with 4 KB block fs, partition
/dev/md* with 4 KB alignment, and avoid all these issues. Disks aren't
that expensive now.
-- 
Krzysztof Halasa
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