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Date: Fri, 23 Jun 2006 18:29:15 -0500
From: "Matthew D. Fuller" <fullermd@over-yonder.net>
To: Volodymyr Kostyrko <arcade@synergetica.dn.ua>
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Cc: freebsd-scsi@freebsd.org
Subject: Re: ahd(4) poor performance
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On Sat, Jun 24, 2006 at 12:25:06AM +0300 I heard the voice of
Volodymyr Kostyrko, and lo! it spake thus:
> 
>   Script:
> 
> dd if=/dev/zero of=/dev/da0s1b count=20480&
> dd if=/dev/zero of=/dev/da0s1b count=20480&
     [...]

This seems like it would be a record-shattering worst possible case
for the disk.  Since there's no buffering on the raw device, each dd
stomps on the sectors of all the others, and each is writing one
sector at a time, so you're probably eating 8 or 10 rotations writing
each sector along the way.  Heck of a stress, maybe, but I'm not sure
it's all that related to anything the disk will realistically do with
normal load.


-- 
Matthew Fuller     (MF4839)   |  fullermd@over-yonder.net
Systems/Network Administrator |  http://www.over-yonder.net/~fullermd/
           On the Internet, nobody can hear you scream.