A specific example of a disk i/o problem

Bill Moran wmoran at collaborativefusion.com
Thu Oct 1 13:10:45 UTC 2009

In response to Dieter <freebsd at sopwith.solgatos.com>:

> > >> > My question is why is FreeBSD's disk i/o performance so bad?
> > > Here is a specific demo of one disk i/o problem I'm seeing.  Should be
> > > easy to reproduce?
> > >
> > > http://lists.freebsd.org/pipermail/freebsd-performance/2008-July/003533.html

FYI, I thought I'd play around with this some in an attempt to add some
useful information to the investigation.

I can not reproduce the problem at all.  I created a 9G file, did the cat
as described in the above URL, and the man request completed in roughly
the same time it did without the cat running.

Just to mix it up a bit, I tried running ls -R on a large directory tree
while the cat was running as well, and performance did not seem to be
significantly impacted there, either.

I ran the tests on my work machine, which is a Dell Optiplex 960 running
FreeBSD 7.2-RELEASE-p3 i386.  Some relevant dmesg stuff:

atapci0: <Intel ATA controller> port 0xfe80-0xfe87,0xfe90-0xfe93,0xfea0-0xfea7,0xfeb0-0xfeb3,0xfef0-0xfeff irq 18 at device 3.2 on pci0
atapci1: <Intel ICH8 SATA300 controller> port 0xfe00-0xfe07,0xfe10-0xfe13,0xfe20-0xfe27,0xfe30-0xfe33,0xfec0-0xfedf mem 0xff970000-0xff9707ff irq 18 at device 31.2 on pci0
ad14: 476940MB <Seagate ST3500630AS 3.AAK> at ata7-master SATA150

Bill Moran
Collaborative Fusion Inc.

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