From: Stan Hoeppner <stan@hardwarefreak.com>
To: Brian Cain <brian.cain@gmail.com>
Cc: xfs@oss.sgi.com
Subject: Re: Consistent throughput challenge -- fragmentation?
Date: Mon, 25 Feb 2013 15:39:54 -0600 [thread overview]
Message-ID: <512BDA2A.5050600@hardwarefreak.com> (raw)
In-Reply-To: <CAEWpfG_DKJt1MmWS1tARH4OmYwpSt=A-DzwKkGcD67LuR6k=Bg@mail.gmail.com>
On 2/25/2013 10:01 AM, Brian Cain wrote:
> All,
>
> I have been observing some odd behavior regarding write throughput to an
> XFS partition (the baseline kernel version is 2.6.32.27). I see
> consistently high write throughput (close to the performance of the raw
> block device) to the filesystem immediately after a mkfs, but after a few
> test cycles, there is sporadic poor performance.
>
> The test mechanism is like so:
>
> [mkfs.xfs <blockdev>] (no flags/options, xfsprogs ver 3.1.1-0.1.36)
> ...
> 1. remove a previous test cycle's directory
> 2. create a new directory
> 3. open/write/close a small file (4kb) in this directory
> 4. open/read/close this same small file (by the local NFS server)
> 5. open[O_DIRECT]/write/write/write/.../close a large file (anywhere from
> ~100MB to 200GB)
>
> Step #5 contains the high-throughput metrics which becomes an order of
> magnitude worse several test cycles after a mkfs. Omitting steps 1-3 does
> not show the poor performance behavior.
>
> Can anyone provide any suggestions as to an explanation for the behavior or
> a way to mitigate it? Running xfs_fsr didn't seem to improve the results.
The usual cause of such aged filesystem low performance is free space
fragmentation. xfs_fsr will defragment files, but in doing so it
*increases* free space fragmentation, thus won't help the situation.
> I'm happy to share benchmarks, specific results data, or describe the
> hardware being used for the measurements if it's helpful.
Paste the output of 'xfs_db -r -c freesp /dev/[device]' just before you
do the large file write. This will show us the free space distribution
histogram.
--
Stan
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next prev parent reply other threads:[~2013-02-25 21:40 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-25 16:01 Consistent throughput challenge -- fragmentation? Brian Cain
2013-02-25 21:39 ` Stan Hoeppner [this message]
2013-02-25 22:06 ` Brian Cain
2013-02-25 22:38 ` Brian Cain
2013-02-25 22:16 ` Dave Chinner
2013-02-25 22:18 ` Brian Cain
2013-02-25 22:23 ` Brian Cain
2013-02-25 23:46 ` Dave Chinner
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