linux-ext4 - Re: Filesystem writes on RAID5 too slow

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Message-ID: <20131119004140.3fea96df@natsu>
Date:	Tue, 19 Nov 2013 00:41:40 +0600
From:	Roman Mamedov <rm@...anrm.net>
To:	Martin Boutin <martboutin@...il.com>
Cc:	"Kernel.org-Linux-RAID" <linux-raid@...r.kernel.org>,
	"Kernel.org-Linux-XFS" <linux-xfs@...r.kernel.org>,
	"Kernel.org-Linux-EXT4" <linux-ext4@...r.kernel.org>
Subject: Re: Filesystem writes on RAID5 too slow

On Mon, 18 Nov 2013 11:02:15 -0500
Martin Boutin <martboutin@...il.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=128,stripe-width=256.

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

> The command line for measuring filesystem read and write speeds was:
> 
> $ dd if=/tmp/diskmnt/filerd.zero of=/dev/null bs=1M count=1000 iflag=direct
> $ dd if=/dev/zero of=/tmp/diskmnt/filewr.zero bs=1M count=1000 oflag=direct

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

-- 
With respect,
Roman

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