From: CZIWKGA@VMSFE.ULCC.AC.UK ("Kevin Ashley, Systems Development, ULCC")
Newsgroups: comp.os.vms
Subject: Summary: Using Micro Technology Exabyte 8500 in low density
Date: 28 Jul 92 14:46:00 GMT
Distribution: world
Organization: The Internet

Thanks to all who responded to my question regarding the use of Exabyte
8500 drives supplied by Micro Technology to write low-density (2.2GB)
tapes. Although no-one was able to solve my problem, your responses
convinced me that I have an issue to raise with Micro Technology here
in the UK.

To remind you of my situation, the drive is connected via a QBUS interface
to a Microvax 3600. The interface must, I presume, perform some intelligent
conversion, making the drive appear to be a TU81 to the QBUS, but speaking
SCSI commands to the Exabyte. Some peoples's suggestions were, unfortunately,
specific to different controller suppliers or to different environments,
such as those where the Exabyte is connected to a SCSI bus on a VAXstation.

Most everyone suggested using INIT/DENSITY=1600 for low density and
INIT/DENSITY=6250 for high. This had occurred to be before I sent my message,
and I probably should have said so. I had tried it, and it doesn't work.
SHOW DEVICE always reports that the drive is operating at 1600 bpi, but
in fact it is always writing high density tapes. However, it is clear
that this is how it is meant to behave. One responder commented that the
firmware needed to be at the right rev level for this to work. This could
be our problem.

Others suggested initializing a tape in the low density drive we have, and
then using it in the high density drive, without rewriting the label - that
is, specifying /NOREWIND to BACKUP, since that is my main use of it. I had
tried this as well. It also didn't work. One responder said that, for
this to work, one had to prevent the tape being rewound after the reading
of the label. BACKUP always seems to rewind the tape to perform label
verification, and although the drive indicates that it is in low density mode
when reading the label, it then switches to high density mode when writing
begins. (I assume this from looking at the Tape Remaining indicator, which
reads in Mbytes remaining.) It may be that BACKUP will perform differently
if there is an empty saveset first on the tape, rather than just labels.
I will try this as well.

However, it seems clear that we really need to get the controller up to rev,
since using INIT/DENSITY works for so many other people. Thanks to all of
those who took the time and effort to respond to my question, specifically:

russell@org.erim (John Russell)
Richard Seymour <seymour@edu.washington.u>
COLOMBO@gov.fnal.fndcd (Rick 'VMS lives 4ever' Colombo)
fox@edu.msu.nscl.rudolf (Ron Fox)
daveg@com.clearpoint.prowler (Dave Goldblatt)
Jim Ross <ROSSJI@mil.af.js-jtf>
Roy Omond <Roy.Omond@DE.EMBL-Heidelberg>
John Macallaster <macallstr@vax.ox.ac.uk>

and others whose addresses I have lost - apologies.
------------------------------------------------------------------------------
Kevin Ashley                              K.Ashley@Ulcc.ac.uk
Systems Development Group Manager         Telephone: +44 71 405 8400
University of London Computer Centre. 

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