Pertec Tape Drive Interface Musings

[Chuck Guzis]

On 08/04/2015 06:17 PM, jwsmobile wrote:

> I was on the SCSI committee when the tape commands were proposed. The
> original that was proposed was to only have a commands which would be on
> disk controllers (who were the main players) to perform backups of disk
> units and restores.  Luckily that effort was headed off by having
> several parties who made tape devices other than Archive join the
> committee.

I know the feeling from my short time with X3J3 (Fortran (was supposed 
to be 88, but became 90)).  The reps from DEC and IBM both threw a hissy 
fit and threatened to withdraw if the committee didn't ratify their 
particular extensions.  It was not a nice experience.

It's really odd that the raw Pertec-style interface, even with its 
various vendor extensions, is still more robust and versatile than the 
SCSI version.  On the other hand, the SCSI standard (X3T10?) does a 
pretty good job of generalizing tape robots.

> Amazingly I've never had a 4mm or 8mm tape fail to read for media
> reasons.  I'm going on having media from both that are as old as the
> technology.  My 8mm backups have only one bad tape in the pile, and it
> was marked as written "incomplete" and bad at the time of creation. Half
> inch I've had the same problems documented with the quality of the
> media, but it is much older.

Wasn't Exabyte the only vendor of 8mm tape backup?  I've seen other 
brands but they all seemed to have Exabyte internals.  4mm DLT is/was 
remarkably robust, particularly when you consider the mechanical 
intricacies.  I was really surprised to see the medium extended to 
DAT-320.  Apparently, there's yet another generation in the works.

On the other hand, the consumer-level tape backups are really terrible; 
Travan, DC-2100, etc.  The worst of the bunch was the Datasonix Pereos 
that used a (wait for it!) 2mm tiny tape cartridge that one had to order 
from Datasonix via Fedex.  Thankfully, that one was brief.

--Chuck