Are old SCSI tape drives not all created equal?

Chuck Guzis cclist at
Wed Aug 17 14:38:35 CDT 2016

On 08/17/2016 11:07 AM, js at wrote:

> I'm experimenting with various old SCSI tape drives to see which will
> work with my PDP-11/34 with an Emulex SCSI card.
> To my surprise, not all SCSI tape drives are created equal.  I was
> under the mistaken assumption that all SCSI tape drives would pretty
> much be abstracted the same way by the SCSI interface.

Well, let's get to the nub of things--exactly what commands aren't
supported in each particular drive?  At a minimum, they should all
provide a response to an "IDENTIFY" command.

6-byte CDBs for read and write are probably supported across all drives
as well, though there are some cases of special "flags".

REWIND should be supported and possibly SPACE commands.  After that,
it's a craps shoot.  Not everyone adhered to the ANSI spec.

Back when I was writing forensic tools, I had to deal with a wide range
of SCSI drives.  I quickly learned to pare my command set down to a
minimum and how to deal gracefully with unsupported features.

Andy Johnson-Laird used to refer to "SCSI Voodoo" and he wasn't far off
the mark.


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