Tape Drives Under 4.2

[rick at seismo.UUCP]

	We have been trying to get two tape drives to run under 4.2 UNIX
	(both TU-78s) without much luck.  For weeks, we have been unable
	to open the drive, although it is recognized at boot time.  The
	DEC man swears that it is functioning properly (although the first
	time he did this, it turned out not to have been initialized), but
	our machines only recognize one of them.

	We have two machines, a 780 and a 750, which are both connected to
	the two drives.  While both machines recognize both drives at boot,
	I can only open drive 0 (drive 1 is not accessible from either
	machine).  The config file (both machines) contains the following lines:

	master		mt0	at mba? drive ?
	master		mt1	at mba? drive ?
	tape		mu0	at mt0 slave 0
--->	tape		mu1	at mt1 slave 0

Your problem is that you have configured both  drives as slave 0. If you
change the second drive to be slave 1, everything should work.

The driver assumes that all of the slave numbers are unique, regardless of
the number of controllers you have. It has an table for mapping minor device
numbers to tape unit numbers. What is happening is that the entry in the
table is "0" for each unit, despite the fact that they are on seperate
controllers. So every reference to mt1 is actually a reference to mt0!

You "should" be able to call them both unit 0 since, they are on seperate
controllers, but you can't. This problem only shows up if you have two
of the same type controller.

---rick