From: crash@ckctpa.UUCP (Frank "Crash" Edwards)
Subject: Re: Amiga Unix Tape
Date: Tue, 10 Nov 1992 03:25:25 GMT
Reply-To: crash%ckctpa@tct.com (Frank "Crash" Edwards)
Organization: Edwards & Edwards Consulting

2575brooksr@vms.csd.mu.edu writes:
>	What inexpensive SCSI drives support the format that the Amiga
>Unix tape comes in?  Thanks!

    "A Question.  Since before the dawn of your race; and before you grew
    upright and walked the face of your planet, I have awaited a Question."
	    -- Star Trek, "City on the Edge of Forever"

    Or something like that -- I forget exactly.
    Sorry about the length of this one folks.  I got a little long
    winded, but reading back over it I don't see anything I want to
    take out.  Well, maybe just a snip here and there.

The installation media is provided in what some vendors call "stacked"
format.  This means that each component of the system is cpio'd
together and written to tape.  Between consecutive cpio archives is a
filemark (qv) which delimits the archives.

The physical media is blocked at 512 bytes, fixed record lengths.
Most QIC tape drives will default to this format and can therefore be
used to perform an installation.  There are some differences between
the implementations of SCSI in some vendors' firmware, however.

Most any drive that defaults to 512-byte blocks will work, one way or
another (see the last paragraph, below).  Commodore supports the
Wangtek, Sankyo, and Caliper tape drives (am I missing one?).  My
patched tape driver adds support for the Archive Viper (and reports
indicate it works with CDC tape drives as well).

Which ones are cheap?  It varies from day to day.  Check "Computer
Shopper" or some such trade rag.  I'm buying a Viper for work at $325.
I never hear anything but good about Archive, and I haven't had
trouble with my drive -- ever -- and I've had it 5 years (or so).

For those with insomnia or a taste for trivia, you might like to read
the following text.  Others can just hit 'n' now.

(This is going to sound a lot like the current "Class 2 Fax" problem!)

Before the SCSI spec was voted into concrete, a few manufacturers
started putting out products that adhered to the "draft" version of
the spec.  These vendors are said to use "Emulex code" because a
quick-to-market firmware was written by a company called Emulex
(they're still in business, are they not?).  Well, when the spec
finally passed the balloting process, the spec had changed slightly
and the firmware developed by Emulex was deemed to be "in spec" but
on the fringes (they made sure that the spec was broad enough to
allow what Emulex had implemented to continue to be correct).

<snip-snip>

In most cases this didn't matter.  But there are a few areas where this
compatibility is an issue:  in the extended sense result from REQUEST
SENSE, bytes 8 through 11 are defined to have a particular meaning for
only *some* of the SCSI commands (such as COPY and SEARCH).  Any other
use of those bits is device- and product-specific.  The Emulex code uses
bitfields within those bytes as status indicators.  That means that any
device which _does_not_ returns the same bits in those locations won't
work with the Commodore tape driver. 

My Archive Viper 2150S was such a device.  It uses those bytes for
their defined purpose and sets them to zero otherwise.  (The CDC spec
says that their devices do this always, but I haven't verified that.)

Since the Viper is a popular drive, since it didn't/won't significantly
cut into the sales of the A3070, and since I have this intense desire
for fame and fortune :-) I wrote patches for the tape driver to function
with the Viper.  Those patches are available in the form of an executable
on the install floppy (thanks to Jan Carlson who lobbied endlessly for
that little contribution!) and as part of the "conf" package in source
form.  The executable only patches the Unix kernel (via /dev/kmem)
enough to READ the tape, not to WRITE to it!  In order to write to the
device, you'll need to install the "conf" package, install my patches
(in the /usr/sys/amiga/alien/contrib directory), and rebuild the kernel. 

<snip-snip>

> Ryan K. Brooks                        "You're never dead till you're        
> 2575BrooksR@vms.csd.mu.edu                  out of quarters."     

Thad has gobs more detail ("gobs" is a technical term -- it means "a lot")
on the specs for various tape drives.  If you need details, mention his
name in the Subject line -- that should get his attention.
-- 
Frank "Crash" Edwards            Perceptual Technologies, Inc.
Fax:  813/786-6526               [Our office is moving; watch this space
Home: 813/786-3675               for the new phone number.]