[rescue] Wide disk on Narrow bus, reprise

[Mark]

On 9 Feb 2008, at 17:39, Curious George wrote:

> Hi, Mark,
>
> --- Mark <md.benson at gmail.com> wrote:
>
>> I have quite a bit of experience of using wide discs
>> on narrow busses,
>
> Great!  :>
>
>> mostly in Macs and Amigas. In my experience, you
>> need to get hold of 2
>> things - a terminator for the end of the 50 pin
>> ribbon (and a ribbon
>
> Why does the ribbon need an extra terminator?

Wide drives don't have onboard terminators. 50-pin busses must be end  
terminated (68-pin ones seem to work both ways in my experience  
however, possibly they work LVD terminated and/or SE unterminated??).  
I know that all the issues I've ever had getting wide drives working  
that weren't down to dodgy Dell/Compaq firmware were usually to do  
with not having terminator. You can substitute the terminator for a 50- 
pin device with one onboard (how they would be setup from the factory)  
but as the LX (AFAIK) ha

>> That's my 2p worth.
>
> It's my understanding that the drive should request
> wide transfers (negotiation) and, if the host
> declines, fall back to narrow.  I.e., I don't see
> anything *wrong* with the approach I have taken...

I think the upper byte terminators in the adapters I have force the  
drives down to Narrow mode by default, because the upper btye is  
terminated at the back of the drive, and so no signal is passed  
through it. I do have some adapters that aren't upper byte terminated,  
come to think of it, that seem to work in most circumstances, but if I  
know the machine is picky I'll use the upper byte terminated ones.

> I'll have to dig through the Standard to see how
> much of this is "optional" vs. mandated.

The biggest issue is SCSI is a non-standard standard. Controllers,  
cabling, etc. vary so much between machines it's a black art getting  
some of them to work. Sun stuff seems pretty hardy SCSI-wise. I've  
hardly had any problems that weren't due to PEBCAK :).


-- 
Mark Benson

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