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Date: Sun, 26 Dec 2010 19:12:37 -0800
Message-ID: <AANLkTi=O+jZoo9K3idxMTHfd-dCBr-8Gd-+sDjHg6hor@mail.gmail.com>
Subject: Re: Slow disks.
From: Mark Knecht <markknecht@gmail.com>
To: Rogier Wolff <R.E.Wolff@bitwizard.nl>
Cc: Jeff Moyer <jmoyer@redhat.com>, Greg Freemyer <greg.freemyer@gmail.com>,
        =?UTF-8?Q?Bruno_Pr=C3=A9mont?= <bonbons@linux-vserver.org>,
        linux-kernel@vger.kernel.org, linux-ide@vger.kernel.org
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On Sun, Dec 26, 2010 at 4:34 PM, Rogier Wolff <R.E.Wolff@bitwizard.nl> wrote:
> On Sun, Dec 26, 2010 at 03:38:51PM -0800, Mark Knecht wrote:
>> First, the drives are 4K sector so it's really important to get them
>> on the right partition boundary. Installing Gentoo requires that we
>> un-tar some large-ish files. IIRC on a 512 byte boundary these drives
>> took 20-30 minutes to do this. On a 4K boundary they took about 1
>> minute. I know that doesn't make sense but those were my numbers, and
>> it's a very high end Intel i7-980x MB so there wasn't any other
>> problem I could find.
>
> Mark,
>
> Thanks for your contribution. You're seeing a 20-30 fold performance
> issue, where only about 2x would be expected. So to test this theory
> I'll see if we can evacuate a partition, untar a large-ish file as a
> benchmark, and then see if we can improve that by changing the
> alignment of the partition. (hmm. Maybe we should do things the other
> way around. First find a tar-workload that takes about 1 minute on a
> properly working drive, and then we can wait up to 30 minutes for it
> to finish on the improper setup.).
>
> Being able to reproduce a problem at will is a great progress to being
> able to solve it!
>
>        Roger.

I hope my memory isn't way off on those numbers. I can certainly
recall that the difference was remarkable and was very easy to
demonstrate.

1) Partition the disk with fdisk placing a partition at sector 63, the
typical first address we're given. Untar a Gentoo Stage 3 release
snapshot such as

http://gentoo.osuosl.org/releases/amd64/current-stage3/stage3-amd64-20101223.tar.bz2

2) Create a second partition starting at sector 1000 and do it again.

It was day and night.

If it was only the performance difference that would be one thing but
the problem i had with these WD10EARS drives was sometimes they would
just hang for long periods. In a RAID they just got kicked.

The kernel was modern for the time I was building the machines, maybe
7-9 months ago.

Hope this helps,
Mark
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