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Re: 2 question about XFS fragmentation and _fsr: SPLITTED Q1:sparse file

To: Janos Haar <janos.haar@xxxxxxxxxxxx>
Subject: Re: 2 question about XFS fragmentation and _fsr: SPLITTED Q1:sparse files
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Wed, 27 Apr 2011 15:18:33 -0500
Cc: Dave Chinner <david@xxxxxxxxxxxxx>, linux-xfs@xxxxxxxxxxx
In-reply-to: <45DD2814B0C84BF3AFD76721A0178E50@myXP>
References: <DFA094D472104424BEA7AA9060DE0D6F@myXP> <20110411214238.GE21395@dastard> <45DD2814B0C84BF3AFD76721A0178E50@myXP>
User-agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; en-US; rv:1.9.2.15) Gecko/20110303 Thunderbird/3.1.9
On 4/26/11 4:51 PM, Janos Haar wrote:

<snip>

>>> In the result, actually we have >6TB images on the 3TB disk, wich is
>>> 97.9% fragmented.
>>
>> How are you determining that figure?
> 
> [root@UNISTORE admin]# cat xfs_get_frat_ratio
> echo loop0
> xfs_db -c frag -r /dev/loop0
> [root@UNISTORE admin]# ./xfs_get_frat_ratio
> loop0
> actual 7650952, ideal 752501, fragmentation factor 90.16%

so you had 7650952 extents on the fs, ideally you'd have 752501, or so xfs_db 
says...

Another way of looking at this is that you have about 10 extents per file on 
average.

Depending on the size of the files, this may be perfectly fine.
Is, for example, a 10G file in ten 1G extents really a problem?

I doubt that fragmentation is your performance problem here.

-Eric

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