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read slower than write on "mv"?

To: xfs@xxxxxxxxxxx
Subject: read slower than write on "mv"?
From: Michael Monnerie <michael.monnerie@xxxxxxxxxxxxxxxxxxx>
Date: Mon, 3 May 2010 10:54:28 +0200
Organization: it-management http://it-management.at
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This is not XFS specific, I see it on every filesys. I do a 
"mv . /newlocation" and see this with iostat:

Device:         rrqm/s   wrqm/s     r/s     w/s    rkB/s    wkB/s avgrq-
sz avgqu-sz   await  svctm  %util
xvdb              608,60    2,60 25967,20   102,40    85,31     5,37    
8,77   1,58  96,72
xvdg              0,00  608,60     0,00 26532,10    87,19     7,55   
12,41   0,12   7,44

Reading takes 97% I/O time, writing 7%. This is on the same raidset, but 
I see the same when copying between two different single disks also. Or 
is it just an effect of write caching that writes look faster than 
reads?

-- 
mit freundlichen Grüssen,
Michael Monnerie, Ing. BSc

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