From: bleau@umdsp.umd.edu
Newsgroups: vmsnet.misc,comp.sys.dec
Subject: VS3100-76 SCSI disk locks up
Date: 10 Nov 92 21:28:51 GMT
Reply-To: bleau@umdsp.umd.edu
Organization: University of Maryland Physics Dept., College Park, MD

Hello, DEC workstation users.  I have a problem that's been bothering me for
some time, and I can't seem to get a handle on it.  First, the configuration. 
I have a VAXstation 3100 model 76, 32MB memory, with a RZ5x internal disk
(200MB+, I forget just which model number), a TZ30, and exteernal hard disk
(1.2GB), and an external rewritable optical disk.  The two external disks were
packaged for us by American Digital Systems; they're sold under the name
MasterDisk.

Now for the problem.  Normally everything works great, but when I do a lot of
transfers of data between the external hard disk and the optical disk (same
SCSI bus) the system slows down and eventually locks up.  Everyone accessing
the external hard disk gets hung, detached jobs eventually hang, and I start
getting calls from everyone and his brother asking what is wrong.  The only way
out of the situation I can find is to (shudder) press Halt and boot the system
from scratch.  Not a nice situation, as you can imagine.

This has shown up in only two applications so far: backup and archiving.  Both
times there is data being copied from the external hard disk to the optical
disk.  It has never happened (I'm not saying it can't, though) on transfers
between the internal (system) disk and the optical disk.  Backing up I have
control over.  Archiving user data files, however, is done under user control,
not mine, and he's brought the system to its knees several times already.

Don't do a lot of data transfers, you may say.  That means not doing backups
onto a fast media, and backing up onto 12 TK50s just doesn't cut it.  Also, one
reason we got this system is to distribute data to other sites.  This problem,
then, hurts us in a big way.  Finally, we have a dedicated line going into this
system to receive data, and the system is supposed to be up 100%, or we miss
some data.  So having it die in the middle of an incoming data transfer is very
messy.

Now you know the outlines of the problem.  I'll spare you the details, as there
are over 1000 lines produces by ANAL/ERROR for just the 24 hrs preceeding the
last crash.  There are, however, a few lines in the error log that I haven't
seen anywhere else, so I'll include the English line output by ANAL/ERROR in
case any body recognizes it.  If you need more info on these specific error log
entries, email me and I'll be happy to send them to you, but they shouldn't be
posted.  Here are those few tidbits:

         SCSI BUS PHASE ERROR
         PHASE CHANGE TIMEOUT DURING DATA IN
         SCSI BUS PHASE ERROR
         TIMEOUT WAITING FOR PHASE INTERRUPT
         BUS BUSY
         BUS RESET INITIATED
         CHECK CONDITION
         UNIT ATTENTION
         POWER ON OR RESET OCCURRED
         PHASE MATCH

One more fact (here's the kicker): recently this same thing happened on a
VAXstation 4000 model 60, with an identically configured (except for SCSI ID
numbers) external hard disk and optical disk.  So while it's been observed for
the most part on the VS3100, it is not limited to that system.  Same situation
on the VS4000: I was doing a backup and the system hung.  Fortunately, though,
the backup on the VS4000 detected a large error count (or whatever it does) and
stops, asking me to specify QUIT or RESTART.  It was getting hairy, as the
optical drive is the _only_ backup device I have on the VS4000!  I had to keep
powering the drive off then back on and telling BACKUP to RESTART before it
would complete the saveset (it took 6 sides!).

I've thought about it being a design problem with the American Digital Systems
disk subsystem, but if that were the case I should see other errors in normal
operations (like bad blocks?), shouldn't I?  I don't see any.  I've also
thought, based upon the wording of the message output by ANAL/ERROR, that it
might be a design problem with DEC's SCSI controller on the VS3100-76 (hence my
cross-posting this to comp.sys.dec), but then why would it also show up on the
VS4000-90?  And why later, too, after several months of operations?

Anything you can say to shed light on this will be appreciated.  In the
meantime I'm limping along with minimal backups and keeping a watchful eye on
the error count, and trying to find some workaround.  Thanks.

Larry Bleau
University of Maryland
bleau@umdsp.umd.edu
301-405-6223
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