List Archive: gentoo-sparc
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From: Derek Pizzagoni <pizz@...>
Date: Wed, 31 Aug 2005 16:09:49 -0700
> As you can see, the drives are identical. The first one comes up in
> mdma2 mode, and the second one comes up in udma4 mode. This makes
> sense, since the motherboard doesn't support the faster interface (only
> up to 33, right?).
The limit is mdma2 mode for the onboard IDE controller.
> I've run them multiple times, and it always comes out similar to above.
> This is on a relatively dormant system. Can anyone tell me why a drive
> plugged into the motherboard's IDE interface (running in mdma2 mode)
> would outperform the same drive plugged into an Ultra66 card (running in
> udma4 mode)? With these results, I'd be better off putting the second
> drive back on the chain with the CDROM.
If there is any noise on the cable, UDMA performance can suffer
dramatically, because commands will be retried when parity errors
are detected on the bus.
It's nice that UDMA handles parity errors nearly transparently
like this, but it can be a silent performance killer.
Another possibility is that the promise driver isn't optimized
for sparc64 so well. This kind of thing has been discovered
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