Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!yale!mintaka!bloom-beacon!primerd!barry
From: barry@primerd.prime.com
Newsgroups: comp.sys.mac
Subject: Help Needed on SCSI Hang
Message-ID: <160700094@primerd>
Date: 8 Mar 90 17:08:00 GMT
Lines: 72
Nf-ID: #N:primerd:160700094:000:4064
Nf-From: primerd.prime.com!barry    Mar  8 12:08:00 1990


I recently added a Maxtor 3280 (240MB) drive to my 4MB Mac SE with an
internal HD20 running 6.0.2; both of these drives use Silverlining 5.2.
Since the Maxtor is one that Prime Computer used as part of a disk
qualification program, I decided it would be prudent to have it running
only when I was actually using it - perhaps 10 hours per week.  The Maxtor
disk has a sealed mechanism, so it isn't subject to the startup "stiction"
problems that plague drives such as the Quantum that use lubricated media.

The Maxtor is terminated with an external terminator that connects between
the end of the cable and the disk.  The cable is a 3ft 25/50 SCSI cable
connected to a 6ft 50/50 SCSI extension cable (I sometimes bring home a
Syquest drive and this cable arrangement makes it easier to connect the
internally terminated Syquest).  Since the Maxtor is fairly loud, the 9
feet of cable let me position the drive so as to minimize the noise from
it.

I've discovered that I can leave the Maxtor connected to the SE and boot
the SE with the Maxtor turned off.  There are no obvious booting problems
if I leave the Maxtor turned off and the SE works fine.  When I want to
use the Maxtor, I turn it on and use the SCSI Probe CDEV to do a SCSI bus
reset and to mount the auto-mount partitions on the Maxtor.  After doing
this, I can use the Maxtor just as if it had been turned on when I booted
the system.  The Cirrus Volumes DA provided with Silverlining works fine -
there are no problems mounting or dismounting partitions.

When I'm finished using the Maxtor I unmount the partitions and turn off
the drive.  This is where the problem arises ...

I've discovered that if I restart after having turned off the Maxtor, the
SE hangs during the boot sequence.  This happens both when I do a Restart
or a Shutdown followed by a Restart.  Sometimes it hangs while displaying
the "smiley Mac" and sometimes it hangs displaying "Welcome to Macintosh".
During a normal boot, the "Welcome" screen appears about a second or two
after the "smilely Mac" screen.  In a reboot after turning off the Maxtor,
the "smilely Mac" screen often displays for 10-20 seconds, during which
time there is heavy activity on the internal hard drive.

I've tried doing a shutdown after powering down the Maxtor followed by a
power off/on sequence on the SE.  This only works if I let the Mac sit
with the power off for more than about 5 minutes (could there be a
capacitor that has to discharge?).  The only other _sure_ cure seems to be
shutdown the Mac, turn off Mac power, disconnect the SCSI cable from the
SE, power on (this results in a normal boot), shutdown, power off,
reconnect the cable, power on.

I thought that there might be an issue with powering the terminator, so I
brought home the internally terminated Syquest drive I use at work and
changed the hookup to be SE <-> Maxtor <-> Syquest. In order for this
configuration to work, the Syquest drive has to be powered on.  When I
retried the Maxtor startup & shutdown sequences described above, I got
the same type of SE hang when I did a restart/shutdown and the same
remedies were effective.  This would seem to rule out powering of the
terminator as a factor.

The really funny thing is that I'm pretty sure (can't be positive) that
when I first started using the Maxtor in early January I was able to
reboot normally after turning off the Maxtor.  I'm looking for help in
figuring out what might be causing the hang and what might have changed
since January. Why is turning off power on the Mac for less than 5 minutes
not effective whereas disconnecting the cable is?

Thanks in advance for any light that can be shed on this mystery.

Barry

s------------------------------------------------------------------------
Barry Wolman                      | barry@s66.prime.com
Principal Technical Consultant    | 500 Old Connecticut Path
Prime Computer                    | Framingham, MA 01701
                                  | 508/879-2960, ext. 1100
------------------------------------------------------------------------