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Date:      Mon, 1 May 2000 18:40:46 -0700
From:      Dragos Ruiu <dr@dursec.com>
To:        ddw@NSMA.Arizona.EDU, Doug Wellington <ddw@NSMA.Arizona.EDU>, freebsd-questions@freebsd.org
Subject:   Re: How many PCI slots can I really use in an Asus P3B-F motherboard?
Message-ID:  <0005011848490B.20353@kyxbot.zorg>
In-Reply-To: <200005020026.RAA16609@cortex.NSMA.Arizona.EDU>
References:  <200005020026.RAA16609@cortex.NSMA.Arizona.EDU>

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On Mon, 01 May 2000, Doug Wellington wrote:
> Hi folks, I've been having some problems with setting up a RAID system -
> everything looked fine at the beginning, but then all kinds of problems
> cropped up and now I'm back to the basics...
> 
> After thumbing through the manual of my Asus P3B-F motherboard, I'm now
> wondering if I can use more than three of the PCI slots...  At first glance,
> it looks like PCI slot 1 shares an IRQ with the AGP slot, and slots 4 and 5
> share an IRQ.  Does that mean that I can't put a card in slot 1 and only one
> card in either slot 4 or 5?
> 
> Any other ideas as to why things would go wrong now instead of right away
> at the beginning?


Keep in mind that theoretical PCI maximum bandwidth is 132MBps and a 
more realistic practical max utilization is about half that.  Two ATA/66 IDE
controllers and about 1.5 (:-) SCSI-UW controllers are sufficient to max it
out.  So if you are building your raid for reliability, stuffing more
controllers on a bus may have some viability, but for performance... more than
two controllers  would seem to be definitely counterproductive.  And who knows,
bus  contention between controllers may be an issue causing some 
problems for you...  throw one or two loaded NICs on the bus in addition
and it sounds like a formula for trouble to me.

cheers,
--dr

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