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Re: XFS defragmentation issue

To: xfs@xxxxxxxxxxx
Subject: Re: XFS defragmentation issue
From: Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx>
Date: Sat, 11 Sep 2010 14:38:48 -0500
In-reply-to: <20100911082330.GG705@dastard>
References: <4C8A4395.5070702@xxxxxxxxxxxxx> <4C8B27E4.2050102@xxxxxxxxxxxxx> <20100911082330.GG705@dastard>
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Dave Chinner put forth on 9/11/2010 3:23 AM:
> On Sat, Sep 11, 2010 at 07:55:32AM +0100, John Lister wrote:
>>  Stan Hoeppner wrote on 9/10/2010 14:00
>>>> On 10/09/2010 15:41, John Lister wrote:
>>> Try unmounting and remounting the filesystem, and see if the various
>>> tools all report the same thing afterwards. This solved the exact same
>>> problem for me very recently, though I'm on kernel 2.6.34.1 and xfsprogs
>>> 2.9.8.
>>
>> Cheers, that got rid of most of it, there is still a slight
>> discrepency  (50 extra fragments) which I can live with.
> 
> xfs_db used buffered IO on the block device, which is not coherent
> with the filesystem. If you are using it on an active filesystem,
> then running "echo 1 > /proc/sys/vm/drop_caches" before you run
> xfs_db should make it read from disk at least once....

That's good to know Dave.  Thanks.  I created a short-name script a
while back with "echo 3 > /proc/sys/vm/drop_caches" merely so I could
"clear the baffles" now and then.  Looks like it now has multiple uses
(if I can just remember to use it in this context).

Out of curiosity, who here schedules automatic xfs_fsr runs, and with
what frequency?  Currently I just run it manually now and then when
performance starts to seem sluggish.

Thanks.

-- 
Stan

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