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Re: nbd vs. failing HDDs (was Re: Status)

On Fri, Sep 09, 2011 at 09:56:20PM +1000, Finn Thain wrote:
> On Thu, 8 Sep 2011, Brad Boyer wrote:
> > I still haven't found the time to get it working in Linux, but I did 
> > find and buy a 100BaseT NuBus card. It even has a chip on it that 
> > appears to be the same one as in some cards that are supported on x86, 
> > so it might even be relatively simple.
> I have one of those cards too but there are more important things to work 
> on first.

True. I'll note that I bought it several years ago and I don't think I've
even taken the time to put it in a computer to see if it works.

> > I don't expect to actually get close to 100Mb/s out of it since NuBus 
> > only runs at either 10 or 20MHz, but it should beat out the 10BaseT 
> > cards.
> Which machines have 10 MHz NuBus, BTW?

Anything that predates the NuBus 90 standard is definitely 10MHz only. I
haven't looked at any newer documentation, but YANCC was Apple's first
NuBus 90 compatible bridge chip and it first shipped in the Q700 and Q900.
Even in that case the processor couldn't access it at 20MHz due to the
design limitations, but as long as it was a NuBus card doing the access
it could use 20MHz. I believe later systems removed this limitation, but
I don't have documentation saying when that happened.

> > The SCSI performance on a Mac depends a lot on the hardware. My IIfx was 
> > so slow that I think I let it run for two days doing a dist-upgrade of a 
> > minimal install. The disks do something in the 100kB/s range as I 
> > recall. Most other Macs are much better.
> Not exactly. Here's the situation:
> NCR5380 chip in PIO mode (as used on IIfx): slow (at best)
> NCR5380 chip in PDMA mode (other early Macs): broken
> DP53C9X chip in PIO mode (as used on 660av & 840av): stable but slow
> DP53C9X chip in PDMA mode (other Quadras etc): stable and fast
> The web site has some info about the individual Mac models:
> http://www.mac.linux-m68k.org/status/

Well, the systems using PIO have real DMA available if we could get
it working properly. The AV systems might be easier since the mac53c94
driver has DMA support, although it would need some changes to work
with the PSC instead of the DBDMA engine of a PowerMac.

Wasn't there some noise about the NCR5380 core being removed entirely
due to using some ancient interface that people wanted eliminated? I
know that it's pretty old code.

Is fixing SCSI high on the list of priorities? I keep meaning to learn
more about SCSI and fixing the NCR5380 driver would certainly encourage
that due to the chip doing next to none of the work itself.

I don't have a lot of time to look at anything, but I am curious what
you see as the highest priorities in case I found more time.

	Brad Boyer

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