Re: SCSI

[Andy Bastien <lists@yuggoth.net>]

Pending further investigation, we now allege that john gennard wrote:
> I've not had anything to do with the Scsi interface. A little while 
> ago in anticipation of trying it, I picked up a PCI board made by 
> Iwill and called a 2930U+ plus a secondhand 2.1Gig IBM OEM 
> harddrive (also a S/H CDRom Drive which I shall leave for the time 
> being).
> 
> There's plenty of literature with the Scsi Host Adaptor - little of 
> which I understand at the moment, but I live in hope. Will a Potato
> installation recognize this board - I haven't yet recompiled the
> 2.2.17 kernel for Scsi so don't know what will be involved.
> 
> The harddrive although old seems in good condition. Again, a
> problem as I can find nothing on IBM's website which helps with
> the jumper settings. There are 12 of these:- 
> 	1. Spare(50pin)
> 	    ID bit3
> 	    (For Wide)
> 	2. ID bit 2
> 	3. ID bit 1
> 	4. ID bit 0
> 	5. Disable Auto Spin
> 	6. SCSI term on
> 	7. Disable unit attn
> 	8. Spare
> 	9. Auto start delay
>           10. Delay start 6/12
>           11. Disable parity
>           12. LED out
> How many jumpers do I need to set? And do I use 4 or 3 if
> the drive initially will be the only device attached?

If it's the only drive or the last drive on the cable, you'll need to
set termination on.  You probably don't want to set any of the ID bits
so that the ID of the drive will be 0.  (The ID bit jumpers set the
device number to 2^x.  Bit 1 makes the drive ID 2, bit 2 makes it 4,
bits 0 and 2 makes it 5, etc.)  The rest of the jumpers you probably
want to leave off unless you have problems with the drive.


> If I can get to understand Scsi and find it a viable alternative to
> IDE, it was my intention to attach a CD writer and some new 
> harddrives externally (the board provides for this). Here again
> I'm lost - some people I've spoken to insist only one device can 
> be attached externally whilst the literature clearly says up to 7.
> Furthermore, here in the UK no-one appears to stock any 'boxes'
> or whatever for more than one device. A stock explanation seems
> to be "haven't seen any for years - there's no call for them" 
> (One 'charming' individual said he knows nothing technical
> about computer parts "I only sell them".

You can attach up to 7 devices to a SCSI-2 chain, and 15 to Ultra SCSI
or better.  Whether they are internal or external is irrelevant,
although you do need to stay within the cable length limitations.
These limitations vary, but, as a rule of thumb, 2m total cable length
is usually fine.  Seagate's website has some good information about
SCSI specs if you want more detail.

There are companies that sell external SCSI chassis over the web.  I
don't know any off-hand, but if search around you'll find them.  There
probably are some within the UK.