From: Roman Mamedov <rm@romanrm.net>
Subject: Re: Filesystem writes on RAID5 too slow
Date: Tue, 19 Nov 2013 00:41:40 +0600
Message-ID: <20131119004140.3fea96df@natsu>
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Cc: "Kernel.org-Linux-RAID" <linux-raid@vger.kernel.org>,
	"Kernel.org-Linux-XFS" <linux-xfs@vger.kernel.org>,
	"Kernel.org-Linux-EXT4" <linux-ext4@vger.kernel.org>
To: Martin Boutin <martboutin@gmail.com>
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On Mon, 18 Nov 2013 11:02:15 -0500
Martin Boutin <martboutin@gmail.com> wrote:

> I have the md0 raid device formatted as ext3 with a 4k block size, and
> stride and stripes correctly chosen to match the raid chunk size, that
> is, stride=3D128,stripe-width=3D256.

What is your stripe cache size?
http://peterkieser.com/2009/11/29/raid-mdraid-stripe_cache_size-vs-write-tr=
ansfer/

> The command line for measuring filesystem read and write speeds was:
>=20
> $ dd if=3D/tmp/diskmnt/filerd.zero of=3D/dev/null bs=3D1M count=3D1000 if=
lag=3Ddirect
> $ dd if=3D/dev/zero of=3D/tmp/diskmnt/filewr.zero bs=3D1M count=3D1000 of=
lag=3Ddirect

Try testing with "fdatasync" instead of "direct" here.

--=20
With respect,
Roman

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