linux-kernel - Re: limits on raid

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Message-ID: <4676C9FF.7060607@redhat.com>
Date:	Mon, 18 Jun 2007 12:07:59 -0600
From:	Brendan Conoboy <blc@...hat.com>
To:	david@...g.hm
CC:	Neil Brown <neilb@...e.de>, Wakko Warner <wakko@...mx.eu.org>,
	linux-kernel@...r.kernel.org, linux-raid@...r.kernel.org
Subject: Re: limits on raid

david@...g.hm wrote:
> I plan to test the different configurations.
> 
> however, if I was saturating the bus with the reconstruct how can I fire 
> off a dd if=/dev/zero of=/mnt/test and get ~45M/sec whild only slowing 
> the reconstruct to ~4M/sec?
> 
> I'm putting 10x as much data through the bus at that point, it would 
> seem to proove that it's not the bus that's saturated.

I am unconvinced.  If you take ~1MB/s for each active drive, add in SCSI 
overhead, 45M/sec seems reasonable.  Have you look at a running iostat 
while all this is going on?  Try it out- add up the kb/s from each drive 
and see how close you are to your maximum theoretical IO.

Also, how's your CPU utilization?

-- 
Brendan Conoboy / Red Hat, Inc. / blc@...hat.com
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