Xref: utzoo comp.sys.mac.hardware:3813 comp.periphs.scsi:605
Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!uwvax!titanic.cs.wisc.edu!tonyrich
From: tonyrich@titanic.cs.wisc.edu (Anthony Rich)
Newsgroups: comp.sys.mac.hardware,comp.periphs.scsi
Subject: Why can't I turn off my tape drive?
Message-ID: <10567@spool.cs.wisc.edu>
Date: 8 Jun 90 10:07:38 GMT
Sender: news@spool.cs.wisc.edu
Organization: U of Wisconsin CS Dept
Lines: 47

I recently put together a Teac 150MB SCSI tape backup unit by mounting a
raw Teac N50 drive in a 5.25" enclosure/power supply.  I've connected
it directly to my Mac II and I use Retrospect to back up my internal
CDC/Imprimis 300MB hard drive onto tape.  The tape drive works properly.

But after doing a backup, if I turn the Teac off while the Mac is still on,
the Mac crashes on the first mouse double-click and won't reboot from the
hard drive; the floppy with the flashing question mark comes up.  Then if
I boot from a floppy, either the hard drive isn't mounted at all or a
dialog comes up with a picture of the hard disk that says "This disk is
damaged; do you want to erase it?"

But if I turn the Teac tape unit back back on and reboot, the hard disk 
WILL then be recognized (even if I haven't repaired it with SUM II yet) and
the Mac will reboot from it, although it takes a while because apparently
some built-in filesystem check-and-repair is done to correct the hard disk's
"damage" before the "Welcome to Macintosh" message comes up.

1.  Is this normal behavior for a Teac 150MB tape backup unit connected to
	a Mac II?  Shouldn't I be able to turn the tape drive off while the
	Mac is on without crashing the Mac?

2.  Since I only do a tape backup occasionally, I don't want to leave the
 	tape drive on forever, although I normally leave the Mac running all the
	time.  Is there some way I can tell the Mac that I'm done with the Teac
	so that I can safely shut the tape drive off without turning off the Mac?

3.  Is there a switch or some other hardware on the tape drive that I can
	or should have modified that will fix the problem?

I don't think it's a SCSI termination problem, but correct me if I'm wrong.
It's my understanding that the Teac N50 has its own internal termination,
and presumably so does the (internal) Wren IV hard drive, so I haven't added
any SCSI terminators, and the tape drive itself functions perfectly.

When I put a Microtek 300Z scanner in the SCSI chain between the tape drive
and the Mac, again with no extra termination, there is no change in behavior;
turning off the tape drive crashes the Mac.  However, I can turn the scanner
(and its special SCSI adapter box) on and off while the Mac is on with no
problems whatsoever.  Why can't I do that with the tape drive?

Thanks in advance for any suggestions.
--
-----------------------------------------
| EMAIL:  tonyrich@titanic.cs.wisc.edu  | 
| Disclaimer:  I speak only for myself. |
-----------------------------------------