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Date: Mon, 18 Jan 1999 10:56:44 +1100
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199901172356.KAA05189@godzilla.zeta.org.au>
To: kpielorz@tdx.co.uk, lcremean@tidalwave.net
Subject: Re: Problems with new IDE's & -current
Cc: current@FreeBSD.ORG
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>> > The machine is a dual P90 (running SMP) - I get the problems even with a
>> > single CPU kernel... It's running Neptune chipset (quite old) - and only
>> > has 1 IDE channel.
>> 
>> I would say that this has something to do with the DMA support, but since
>> Neptune's IDE controller isn't DMA capable and PCI, that doesn't follow.
>> Chances are that there's a not-quite-bad spot on your drive -- does it
>> always seem to happen in the same place on the disk?
>
>Nope, it's more 'load' oriented than 'spot' oriented (i.e. the harder you push
>them - the more of the above you get)... Both drives are brand new out the box
>(for what it's worth), so I doub't they're 'bad'... DMA is disabled in the
>kernel config as well, and the dmesg shows no hints of either multi-block or
>DMA transfers...

New models of IBM IDE drives are fast enough to consume a significant
fraction (perhaps > 100%) of PIO mode 4 bandwidth (16.6 MB/s).  Don't
use them without DMA.  Don't use them without UltraDMA (33.3 MB/s) if
you want full performance.

Bruce

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