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Date: Sat, 21 Aug 2010 19:37:31 +0100
From: Bruce Cran <bruce@cran.org.uk>
To: Steffen Neubauer <stefreak@stefreak.de>
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Cc: freebsd-questions@freebsd.org
Subject: Re: IO fluctuation
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On Sat, 21 Aug 2010 20:29:05 +0200
Steffen Neubauer <stefreak@stefreak.de> wrote:

> So this is not a zfs problem. But I don't think it's the hardware,
> too - I used that mainboard before FreeBSD with no problems.
> And the WD EARS drives can't be the problem on raw device access,
> too, because I used bs=1M, that should be enough...

It _is_ the EARS: the hang is probably the drive spinning back up after
it's turned itself off - it has really aggressive power management by
default. 

For more information about the variation, see
http://maycontaintracesofbolts.blogspot.com/2010/08/benchmarking-advanced-format-drives.html

-- 
Bruce Cran