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Date:      Tue, 31 Dec 2002 16:49:57 -0500
From:      Bruce Campbell <>
To:        Matthew Emmerton <>
Cc:        freebsd-hardware@FreeBSD.ORG, freebsd-questions@FreeBSD.ORG, sos@FreeBSD.ORG
Subject:   Re: ata "fallback to PIO mode" on dual processor AMD systems
Message-ID:  <>
In-Reply-To: <025701c2b112$ddfbf580$>
References:  <> <025701c2b112$ddfbf580$>

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Quoting Matthew Emmerton <>:

> [ cc'ing Soren since he's the ATA guru ]
> > Dec 30 23:27:00 ecserv13 /kernel: ad0: trying fallback to PIO mode
> > Dec 30 23:27:00 ecserv13 /kernel: ata0: resetting devices .. done
> >
> > The test continues to run with the ata controller in PIO mode, with
> > slower performance, and higher load average.
> >
> > Once the master drops to PIO, attempts to access the slave then cause
> > it to drop to PIO.
> Are you using 80-conductor cables on all your drives?  These are required to
> get consistent high throughput, and running without them may cause the
> problems you're seeing.

Thanks for the information about the design of IDE etc, and the suggestion
about the cables.  I was about to shuffle things to get the disks
onto separate channels, but I now see that would be a mistake as my
CD drive would share a cable with a disk.

Anyway, they all have the 80 conductor cable.  I forgot to add some 
environmental and other information.

 The 4 AMD systems are in Aopen hx08 towers, with 400 watt power supplies,
 and 5 auxilliary fans (in addition to the power supply fan, and fan on
 each cpu).  They are in an air conditioned machine room.  The CPU and
 motherboard temperatures are within spec.  I mention this as I note
 many reported AMD system problems traced to overheating.

 All drives are installed in removeable drive bays.  I don't have the make/model
 on hand right now.  They were $19 CAD.  ($13USD).  The low cost makes
 me suspicious now, but...

 I'm running the same tests on 4 single processor 2.4GHz Intel systems.
 They have not failed in this manner so far.

 Initially, I had 1GB memory modules in the AMD systems (I can't remember
 the make) and the systems froze and rebooted randomly.  I moved to
 Crucial 512MB modules to cure that problem.

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