Are old SCSI tape drives not all created equal?

js at js at
Wed Aug 17 16:59:09 CDT 2016

On 8/17/2016 2:38 PM, Chuck Guzis wrote:
> 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.

Hi, Chuck.  Excellent question -- and they do respond per your minimum, but beyond that, I'm not sure.  When a drive wouldn't work, I only thought to check for unit ready, unit identify, and to see what would happen with a START or STOP unit command.

Even the Teac MT-2ST would respond to those 3 (for the START or STOP command, it retensions the entire tape).   Interestingly, the Teac also doesn't provide a unit name like all the others do eg. "ARCHIVE PYTHON etc..."   It just shows up as a blank during bootup on a PC with an Adaptec SCSI card.  This lack of name seems to make it invisible to Windows (XP) ASPI.

I have MSDOS software than allows one to issue direct SCSI commands, but doing that is beyond my present know-how.

Thank you-

> 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.
> --Chuck

More information about the cctalk mailing list