| UltraSCSI disks are indeed supported in old green BA356 shelves - with a
couple of restrictions, though.
Restriction #1 - do NOT connect the shelf to an UltraSCSI adapter - without a
new UltraSCSI personality card you will be exceeding the "speed limit" for
the physical cabling if the adapter and drive try to talk at 20 Mhz. If you
want to run your UltraSCSI disk at UltraSCSI speed you must upgrade to a new
(top-gun blue colored) BA356 shelf with a new (top-gun blue colored) power
supply and a new (same color as before, but smaller connectors) personality
module.
restriction #1a - do NOT put a new personality module in the old BA356 shelf
and think that solves the problem above - the new personality module draws +5V
power (the old ones were passive) and this can cause too much of a drop on the
+5V of the old green power supplies (most drive power is +12V, but some is
+5V). Get a new, blue, shelf.
restriction #2 - and I hope this is temporary, we are still testing - do not
put an UltraSCSI disk in the same green BA356 shelf as a 5.25" SBB. The reason
is given below. You will be able to mix UltraSCSI disks and 5.25" SBB's in
the new BA356 shelves.
I should remind you, at this point, that the UltraSCSI products have not been
announced or shipped yet, so its inappropriate to discuss them in this open
notes file. I am placing a pointer to a draft copy of the UltraSCSI
Configuration Guide in the STORAGE_PRESENTERS notesfile - this is still a draft
(it went out for review today, and of course we are going to wait on the tests
mentioned in restriction #2 before finalizing it) but it is pretty detailed and
(I hope) accurate.
Now, the reason for restriction #2:
Some devices in 5.25" SBB's cause degradation of the electrical environment on
the SCSI bus. This is due to them having too much capacitance (a spec
violation, but they get away with it because - well, its SCSI) and being on a
longer than usual stub (the folded gray cable inside 5.25" SBBs - we also
played a bit fast and loose with the spec here, because - well, its SCSI).
UltraSCSI drives do less noise filtering than Fast SCSI drives - because the
signals are higher frequency, and filtering distorts the signals too much - and
some of them are more sensitive to this kind of stuff. Specifically, UltraSCSI
disks from one of our vendors were showing up sensitive to this, and getting
errors on the bus; even an occasional data corruption. The vendor has
implemented a fix and all RZ1xx products are shipping with that fix, but we
haven't done enough testing to convince ourself that the fix works - it very
well could NOT work in all cases. So until we complete the testing (mid-late
May), this restriction is in force.
Richie
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