Message-ID: <4676C9FF.7060607@redhat.com>
Date: Mon, 18 Jun 2007 12:07:59 -0600
From: Brendan Conoboy <blc@redhat.com>
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To: david@lang.hm
CC: Neil Brown <neilb@suse.de>, Wakko Warner <wakko@animx.eu.org>,
       linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org
Subject: Re: limits on raid
References: <Pine.LNX.4.64.0706141957020.29630@asgard.lang.hm> <18034.479.256870.600360@notabene.brown> <Pine.LNX.4.64.0706142034400.29630@asgard.lang.hm> <18034.3676.477575.490448@notabene.brown> <20070616020320.GB2002@animx.eu.org> <18035.23867.576212.859440@notabene.brown> <Pine.LNX.4.64.0706160037220.7557@asgard.lang.hm> <4676BEC2.7090809@redhat.com> <Pine.LNX.4.64.0706181026170.12717@asgard.lang.hm>
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david@lang.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@redhat.com
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