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Re: cannot defrag volume, fragmentation factor 21.73%

To: xfs@xxxxxxxxxxx
Subject: Re: cannot defrag volume, fragmentation factor 21.73%
From: Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>
Date: Fri, 22 Oct 2010 23:02:38 +0200
Cc: Richard Ems <richard.ems@xxxxxxxxxxxxxxxxx>
In-reply-to: <4CC1638B.4070807@xxxxxxxxxxxxxxxxx>
Organization: it-management http://it-management.at
References: <4CBC3910.70806@xxxxxxxxxxxxxxxxx> <20101018231009.GL29677@dastard> <4CC1638B.4070807@xxxxxxxxxxxxxxxxx>
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On Freitag, 22. Oktober 2010 Richard Ems wrote:
> But, at which numbers should I look at before starting a defrag then?

Watch the performance of your application. Record answer times with 
munin or something, and if you ever "feel" it's too slow, look at the 
recorded numbers again to see if your feelings fit the measurements. 
Don't be paranoid about fragmentation. The more people access a server 
at a time, the less important fragmentation is. 

If you got 100 people streaming 100 perfect defragmented files, you 
still got an access pattern that needs to move the disk head to 100 
different positions all the time. If your single disk can't do that many 
I/O's, build up a RAID, or get faster disks (10kprm, 15krpm, SSD).

Defrag is more for single threaded I/O workloads, where one stream at a 
time has to be read/written. Therefore it helps on a Windows PC more 
than on a server. Only use defrag if you really have lots of chunks per 
file.

-- 
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Michael Monnerie, Ing. BSc

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