linux-ext4 - Re: More testing: 4x parallel 2G writes, sequential reads

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Date:	Thu, 08 Nov 2007 02:17:55 +0300
From:	Alex Tomas <bzzz.tomas@...il.com>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: More testing: 4x parallel 2G writes, sequential reads

Hi,

could you try to larger preallocation? like 512/1024/2048 blocks, please?

thanks, Alex

Eric Sandeen wrote:
> I tried ext4 vs. xfs doing 4 parallel 2G IO writes in 1M units to 4
> different subdirectories of the root of the filesystem:
> 
> http://people.redhat.com/esandeen/seekwatcher/ext4_4_threads.png
> http://people.redhat.com/esandeen/seekwatcher/xfs_4_threads.png
> http://people.redhat.com/esandeen/seekwatcher/ext4_xfs_4_threads.png
> 
> and then read them back sequentially:
> 
> http://people.redhat.com/esandeen/seekwatcher/ext4_4_threads_read.png
> http://people.redhat.com/esandeen/seekwatcher/xfs_4_threads_read.png
> http://people.redhat.com/esandeen/seekwatcher/ext4_xfs_4_read_threads.png
> 
> At the end of the write, ext4 had on the order of 400 extents/file, xfs
> had on the order of 30 extents/file.  It's clear especially from the
> read graph that ext4 is interleaving the 4 files, in about 5M chunks on
> average.  Throughput seems comparable between ext4 & xfs nonetheless.
> 
> Again this was on a decent HW raid so seek penalties are probably not
> too bad.
> 
> -Eric
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