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Re: Fragmentation of Journaling FS

To: Constantin Loizides <Constantin.Loizides@xxxxxx>
Subject: Re: Fragmentation of Journaling FS
From: Utz Lehmann <leh@xxxxxxxxxxxxxx>
Date: Wed, 1 Aug 2001 16:52:46 +0200
Cc: Utz Lehmann <leh@xxxxxxxxxxxxxx>, xfs-list <linux-xfs@xxxxxxxxxxx>
In-reply-to: <3B680A34.C08783AC@xxxxxx>; from Constantin.Loizides@xxxxxx on Wed, Aug 01, 2001 at 03:55:00PM +0200
References: <3B67D35E.64877CBF@xxxxxx> <20010801144322.C1132@xxxxxxxxxxxxxx> <3B680A34.C08783AC@xxxxxx>
Sender: owner-linux-xfs@xxxxxxxxxxx
User-agent: Mutt/1.2.5i
Hi Constantin

Constantin Loizides [Constantin.Loizides@xxxxxx] wrote:
> > I made a quick and dirty test running this:
> > 
> > while time cp -a /usr/src/linux/drivers/ /mnt/xxx-`date '+%s'`; do sync; \
> > df | grep mnt; done
> > 
> Ok, will try this when my test system is available...
> 
> Please notice, that I am using a different setup:
> different version of xfs,
> different file size distribution (i checked that on my /drivers/ dir)
> 
> Can you check your test on a small partition of 512 MB, just to 
> make sure, that it gives the same flatness?

Ok, i have run my test on a 1GB and 512MB volume (using lvreduce).

1GB volume:

user    system  elapsed CPU     Used    Avail.  Use%

0.10    2.55    0:22.01 12%     75100   968676  8%
0.17    2.98    0:22.92 13%     150040  893736  15%
0.09    2.62    0:22.63 11%     224996  818780  22%
0.14    2.77    0:22.51 12%     299952  743824  29%
0.08    3.01    0:23.24 13%     374892  668884  36%
0.10    2.92    0:22.77 13%     449832  593944  44%
0.18    2.89    0:22.95 13%     524772  519004  51%
0.07    3.10    0:22.88 13%     599668  444108  58%
0.09    3.11    0:22.95 13%     674592  369184  65%
0.12    2.78    0:23.20 12%     749516  294260  72%
0.14    3.02    0:23.92 13%     824456  219320  79%
0.14    3.11    0:24.03 13%     899412  144364  87%
0.14    3.29    0:23.91 14%     974304  69472   94%


512MB volume:

user    system  elapsed CPU     Used    Avail.  Use%

0.12    2.60    0:16.69 16%     75100   444388  15%
0.16    2.68    0:17.29 16%     150040  369448  29%
0.09    2.72    0:16.96 16%     224996  294492  44%
0.11    2.61    0:16.62 16%     299904  219584  58%
0.11    2.60    0:16.29 16%     374828  144660  73%
0.12    2.79    0:15.70 18%     449768  69720   87%


No sharp drop.
That the elapsed time is reduced by the volume size is very interessting. On
the 512MB volume it's only half of the 4GB volume. My test is very quick and
very dirty.


btw: For your agesystem you can maybe add following:
- random file deletion
- deletion of whole trees
- simultaneous writing of files (very important, a lot of filesystems are
  fragmenting these files badly)
- appending to files in different sized pieces (like logfiles)


utz


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