Inconsistent IO performance

[Kevin Oberman]

> Date: Sat, 14 Aug 2010 11:06:58 +0800
> From: TJ Varghese <tj at tjvarghese.com>
> 
> >
> 
> > > Maybe there is a hardware component here? Are both disks on the same
> > > controller? Or if not are both controllers using the same interrupt line?
> >
> > No. Each is on its one controller and is the only disk on that
> > controller.
> >
> > > You should have a look at 'systat -vmstat' with dd running in the
> > > background. That might give a clue as to where the bottleneck is.
> >
> >
> >
> You're using a laptop with 2 HDDs, so does that mean you're using the
> Ultrabay for the 2nd HDD?
> Perhaps anything connected to that drops down to ATA33 (pure speculation on
> my part) since it was designed for optical drives ...dmesg/atacontrol logs
> would be useful here.
> 
> You may want to try dd with the of=/dev/null instead to remove the 2nd
> variable and benchmark solely the read speed of the 1st hdd.

For this test I get a very consistent 34.75 MB. (1000 10M
blocks). Distressingly low when there is almost no seek activity.

Nope, it is running at UDMA100 using a SATA-PATA converter. (The ICH6
controller is SATA.) But that was a good idea.
-- 
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634
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