Date: Sat, 21 May 2005 10:08:17 +1000
From: David Elmo <[EMAIL PROTECTED]>
So I am assuming that the 7600 is
supplying the needed power and that I was right to remove it and avoid the
possible "problem" of too many cooks you mention.
The 7600 should definitely supply term power on its SCSI busses. The
only machines that I know of which don't are the Mac Plus and some of
the PowerBooks. I don't remember which Powerbooks, but I know I
would double check that on any of them before assuming that they do.
The two-devices-supplying-term-power situation is not always fatal.
I have no idea how often it is a problem. I suspect rarely.
However, it does cause a problem sometimes. In my case I learned
about it many years ago when I was trying to run an array of ST32550W
(early Seagate Barracudas) and had no end of trouble with them. A
call to Seagate led to the recommendation to disable term power on
the drives, which sounded screwy to me--why would more than one term
power cause a problem--but it solved the problem. I was at the hair
pulling stage as I had SCSI IDs and termination properly set and good
equipment.
On the Apple CDs I have lying about, there are 7 pin pairs, the first three
to the left are supposed to be jumpered. The far right is labelled "TERM
POWER", the others are unlabelled, maybe one of them (probably the one next
to the end right) would be termination.
I suppose this shows the 7600 does supply termination power on its internal
scsi bus? Or does it?
Yes it does.
Oh, another SCSI anecdote. Back around the same time as the
Barracuda problem I had a NEC 3X drive, the type that uses a caddy to
load the CD. That drive would cause problems on the chain unless
there was a disk present in the drive at boot up. That was (I think)
a case of an improperly designed SCSI device, or poor firmware
implementation.
Jeff Walther
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