In March I wrote a post on how I was unable to see my DLT 7000 drive on my
AIX 4.2.1 bus. The drive was a fast wide diff DLT 7000 drive and my server
was a 7013 model J40.
I had two open MD68 connections on the back of my System Card (I.e. the card
that has the keyboard, mouse, and serial connections) and the assumption by
the previous System Admin (and myself also) was that you should be able to
plug into one of these connections, select an unused SCSI ID and properly
terminate the bus. The expectation was that the drive would show up when
configmgr was run.
When I came on the scene and inherited the "problem" I was thinking that I
didn't properly understand the relationship between ascsi0, vscsi0, and
vscsi1 and I had posted some questions etc..
Well, we had a very serious crash about a week ago (lost rootvg) and had to
have some hardware switched out. While the IBM hardware guy was there I
decided to educate myself further on the J40. I must say, it was quite a
It seems that the two MD68 connections on the back of my system board were
not free (I knew that internal devices were using them but I thought I could
chain)! and that I was NEVER under any circumstances to plug anything into
these connectors. It appears that the first connection, labeled
differential SCSI A is used for the internal bus (in my case, 4 hard disks,
a CDROM, and an 8mm Tape drive). The only thing to be attached to this
connection is a Terminator.
The second connection, labeled differential SCSI B, leads to a set of 4
(empty in my case) drive bays where you can put additional disk. Since I had
no disk installed I was to leave this connection unterminated until such
time as I used one of the empty bays.
Conclusion, I cannot use the built in differential SCSI card (ascsi0) for
anything except to load up the "built in" device bays. I had to buy a new
fast wide differential card in order to begin the process of adding new FW
diff devices to my system.
I don't know if this is the same on other "classic" RS/6000 hardware but I
must say I found it beyond strange coming from other UNIX vendor shops where
an empty SCSI slot usually means the ability to chain additional device
provided you have a free SCSI ID available.
Oh well, live and learn. I just thought I would pass this bit of trivia on
to other J40 users.