[SunRescue] Proper use of VME scsi controllers?

[Greg A. Woods]

[ On Tuesday, February 8, 2000 at 17:21:09 (-0500), BSD Bob wrote: ]
> Subject: Re: [SunRescue] Proper use of VME scsi controllers?
>
> Both the sun2 and sun3 controllers I have appear to be standard 2 plug
> vme things.

OK, then you have a 501-1045 Sun-2 SCSI host adapter according to the
old hardware reference FAQ.

> For my built-up adapters, I used the internal/external adapter frames
> from sun2 controllers, and dropped in sun3 controller boards.  That
> gave me both internal and external I/O.  It seems to work fine, but
> does not like long bus lengths, especially on older drives that load
> the bus down.

Use active termination, high-quality cables and connectors, and
terminator power supplied from the ends of the bus.  If it doesn't work
reliably then you almost certainly have a physical problem of some sort.

> My feeling is that the older controllers don't handle bus loading
> very well.  It seems to take more power to drive the transitions
> on the bus with the older full height drives.

That's quite likely.

> For the sake of discussion.....
> 
> 1.  Tape in top bay on one controller, and 4 drives externally on the
>     second controller.  What specific part numbers for the frame adapter
>     should I use on the second controller to keep from blowing it or the
>     backplane, and what slot/busjumpering is required?

You'd want an internal-only controller in slot 7 and an external-only
controller in any other legal slot.

Do you have a copy of the appropriate version of the Field Engineer's
Handbook to help determine the legal slot and to show the backplane and
controller jumpering/switches?

> 2.  Tape and two drives in top bay all scsi, then 4 drives and external
>     tape on the second controller.  How?

Same deal.

The only trick is if you want just one controller for both internal and
external use.  There's an official sun2 "sc" combination that does this
but for sun3 "si" you need to make one up from various parts as I
described in another message.

> On my internal/external hacks, only the tape is inside, and the drives
> are outside in shoeboxes.  The terminators have been removed on the board
> and the tape has one end terminator and the end of the drive chain has
> the other.   Total length about 16 feet of bus, within the 25 foot (6M)
> standard.  It could be that the cabling is pushing things lengthwise
> because of old less than perfect connections and cabling.  I was thinking
> of cobbling up a metal slide plate with mounts for 4 drives internally
> and then using the last slot for that as a place holder.  It would take
> up about 2-3 slots or lose me 10-12.  That would take the cable run off
> the internal header with a relatively short ribbon cable.  Power is
> there aplenty for 3.5 inch drives from the top bay.  The other end
> through the backplane would catch the internal tape.  Would something
> lie that be reasonable?

Anything that reduces the length of the bus and gives you the best
quality in-spec. cable and connectors is a good idea!  ;-)

> I thought it was 6 meters?    I am beginning to think it cabling
> and poor connectors more than anything else.

6m only at 5MHz synchronous for single-ended.

> I have been using passive termination.  I am sensing  that is less than
> optimal?

Passive termination sucks big time.

You need the terminator with the little LED and it must be lit when the
power is on and you should have it on both ends.

-- 
							Greg A. Woods

+1 416 218-0098      VE3TCP      <gwoods at acm.org>      <robohack!woods>
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