[rescue] Wide disk on Narrow bus, reprise

Curious George jorge234q at yahoo.com
Tue Feb 5 18:26:45 CST 2008


Well, I've tried several different ways to get
a wide drive onto a narrow SCSI bus (SPARC LX)
and can't seem to figure out what is going wrong.

The most promising approaches (for mechanical
reasons) used short, in-line adapters to alter
the cabling between the drive and the motherboard.

In the first case, I tried installing a 68pin (M)
to 50pin (M) adapter on the back of the wide drive.
In effect, this made the drive *look* like a
50pin narrow drive.  The short ribbon cable between
the drive and motherboard was then installed.

But, the adapter makes the drive "too long" for
the space available in the LX case (i.e., the
ribbon cable connector sticks out beyond the
plane of the case so closing the case is not
possible -- I have no desire to rework the
sheet metal mounts  :< )

Next, I tried installing a 50pin (F) to 68pin (F)
adapter in the 50 pin header on the motherboard.
Then, running a 68pin cable between the drive's
68pin connector and the 68pin connector presented
by this adapter.

Mechanically, this allows the case to be closed!

But, *electrically*, it's a no-go!  :<  The drive
never appears in probe-scsi.

Note that I had strapped the drive to "FORCE SE
MODE" to ensure it wasn't an LVD vs. SE issue.

I also had a terminator attached to the cable
proximate to the drive (i.e. the cable had a
built-in terminator module that I ensured was
at the drive end of the cable).  So, I am
reasonably sure the high byte (which theoretically
is "floating") *is* terminated.

I also made sure the drive was strapped for a
low SCSI ID (I tried 0, 4, 6).

I also tried *another* wide drive (both drives were
known to be working).

Connecting a regular SE drive to the external
SCSI port proved that the bus was operational
*despite* my modifications dangling off the
internal port.

Unfortunatey, I don't have a protocol analyzer
so I can't see if the host is talking to the
drive at all -- nor how it may be reacting to
"unexpected" SCSI messages (e.g., wide
negotiation requests).

What am I missing?  This *seems* like it should
work...  :<  Anything else I can try?  (annoying
that narrow drives are so damn *small* -- the LX
is such a nice sized/powered box for the purposes
to which I intend it  :<)

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