[Info-vax] AS1200 disk bay question

[Stephen Hoffman]

On 2018-12-26 13:19:34 +0000, Hans Vlems said:

> The split-bus configuration I tried on an Alphaserver 1200 did not work 
> because it took more parts than I had available.
> So the disk bay must revert to a single bus. On the back there are four 
> black connectors that look somewhat like SCA connectors.
> The bottom one connects to the controller (via a piece of hardware that 
> is mounted on the side of the bay).
> The middle two connectors are connected by means of a short pice of plat cable.
> The top connector holds the terminator.
> 
> The console shows only DKC0: thru DKC300: , the other disks are not visible.
> I have no documentation on the diskbay, hopefully someone with a better 
> memory than mine or with a manual can help me??

I've not looked at the back side of the AlphaServer 1200 in an aeon or 
two, though I'd expect it's similar to the canonical BA356 with some 
minor changes for internal mounting.   I'd suspect that the "piece of 
hardware that is mounted on the side of the bay" is the equivalent of 
the BA356 personality module in this configuration, if there's not a 
personality module in the more typical front-mount location and hidden 
under a bezel.  That short piece of flat cabling is probably a cheaper 
version of the jumper board found on the BA356.

Here's the doc on the BA356, and chapter 3 covers the 
split-bus/dual-bus details that'll be interesting here.
https://www.mavin.com/pdf/bu356uga.pdf

The following is from another source:  "To operate BA356 in split-bus 
(odd-numbered disk slots are on one SCSI bus off the JA1 SCSI 
connection, and even-numbered slots are on the other bus via the JB1 
connection), ensure the terminator board is behind slot six and the 
jumper board is behind slot one. These are located behind the fans. To 
select single-bus, place the terminator behind one and the jumper 
behind six. (You'll have to remove the fans to get at these boards.) 
Visible in the back of the disk six and disk one bays, you'll see pins 
protruding through from the back side of the backplane. Each slot as a 
hole labeled T and J, and the pins are T and J on (wait for it) the 
terminator and the jumper board. Based on where you see the pin, you 
can avoid have to remove the fans and look.

The shelf OK jumper is in the disk bay behind slot 2, and the pin 
positions are labeled 1 and 2. Both off prevents the controller from 
processing it. Jumper across 1 is for the dwzzb, and across 2 passes 
shelf OK to the controller. If you have both off, hang the jumper off 
just one of the pins."

If you have both odd and even disks visible, then there's some issue 
other than split-bus arising here.  Possibly incorrect termination.  Or 
some other hardware error.  I've had a few of these boxes fault in 
weird ways, and have had a few disk bricks/canisters/SBBs that have 
hosed the bus.  Or the internal BA shelf in this box is less like a 
BA356 than I'd tend to expect...



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