Are old SCSI tape drives not all created equal?

[js at cimmeri.com]

On 8/17/2016 6:17 PM, Chuck Guzis wrote:
> On 08/17/2016 02:59 PM, js at cimmeri.com wrote:
>
>> 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.
> Well, that's all good.  SCSI tape covers a lot of ground--from 9 track
> 1/2" open-reel drives and includes various technologies, from simple
> DCxxx QIC carts, to DDS, SLT, DLT...  All have their peculiarities.
>
> For example, some permit rewriting of blocks; others put this strictly
> off-limits.  Lots of features are vendor-optional, which include things
> such as partitioned data sets and robot auto-loaders.  Read-after-write
> verification is optional (but is a good thing, particularly if the drive
> firmware includes recovery by erase-and-rewrite.
>
> Linux can be pretty decent about a one-size fits all and has several
> optional packages that people have submitted, including the st toolkit.
>
> If you can program C, I might have some DOS I/O library functions that
> may interest you.
>
> Generally speaking, the "safe, always there" commands are INQUIRY
> (0x12), TEST UNIT READY (0x00), REWIND (0x01), REQUEST SENSE (0x03),
> READ(6) (0x08), WRITE(6) (0x0a)  WRITE FILEMARKS (0x10), MODE SENSE
> (0x1a), MODE SELECT (0x15), UNLOAD (0x1b) and perhaps SPACE (0x11).

Chuck,

   Where might I find information on how to form SCSI command data blocks so as to try the above commands?   I sent just an "01" to the TEAC MT-2ST, and it did rewind.. but did not react to any of the other above commands just by sending single bytes.

   Oddly, the OnStream drive did *not* accept an 01 command.

Thank you-
-John


> Of course, commands such as MODE SENSE, MODE SELECT and REQUEST SENSE
> have variable implementations.  Status for a given condition isn't
> guaranteed to be the same across devices; for instance on the Qualstar
> SCSI half-inch drives like to return a record of zero length instead of
> setting the "filemark hit"  status on a read operation.
>
> Generally speaking, however, as long as you stick to the above list and
> the simplest options, you'll be good with anything.
>
> --Chuck