From: venard@bms.com
Subject: Query re: VMS Backup and robotic tape subsystems
Reply-To: venard@bms.com
Organization: Bristol-Myers Squibb
Date: Fri, 21 Aug 1992 21:59:51 GMT

Here's something:

Does anyone have any first-hand experience with how VMS Backup works with any
of the large capacity, robotic "juke-box" type tape subsystems? 

Basically, these subsystems consit of static "shelves" or "carosels" in which
various quantities of media (3480 or 8mm tape cartridges) are stored. One or
more tape transports are situated in proximity to the tape storage area. A
mechanical "robotic arm" is used to to physically move tapes between the
shelves and the tape transports. This whole rig is self enclosed with a
window in front so the human can watch the action. 

My question is how do these units work with the VMS Backup Utility for VAX
backups? What I am wondering about is, if such a tape subsystem were made
available to a VAX system via an HSC for example, what tells the subsystem
which tape to load into the tape transport next?

For example, in the case of a single reel TA81 subsystem, and VMS Backup, when
the end of the current tape reel is reached, the tape is automatically rewound
and unloaded, and VMS Backup sends a message requesting the Operator to mount
the next tape. The VMS Backup utility polls the state of the tape drive,
detects when the mount request has been satisfied, and then continues with the
backup. 

In the case of a subsystem that uses a magazine containing multiple tape
cartridges, when the end of the current tape is reached, the tape
automatically rewinds and unloads, and, just as before, VMS Backup sends a
message requesting that the Operator mount the next tape. But, in this case
the Operator has no need to do so, as the magazine advances mechanically and
when in position, the next tape is loaded automatically. The VMS Backup
utility detects that the tape has been loaded and continues with the backup,
and so on until the backup is done or the magazine runs out of tapes. 

What I am wondering is how these robotic systems work in this respect. It
would seem to me, not having one and just guessing, that there is no
"magazine" as such. Just a bunch of tapes stored on shelves in the subsystem
enclosure that can be randomly selected by a robotic arm which moves about
vertically and horizontally in the cabinet, based on access commands
transmitted to the subsystem from some external controlling source. What we
would want, ideally, is some way for such a system to "emulate" a traditional
magazine fed system, so we could know based on observed physical positioning
of the tapes on the shelves which tape would be selected first, second, and so
on, and also a way for the subsystem to automatically select from the stacks
and load into the tape transport the "next" sequential tape. 

Can VMS Backup work transparently with such a subsystem, or is it necessary
for a separate command to be sent from the host system to the robotic control
portion of the storage subsystem for each tape selecting and loading
operation? 

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Robert Venard, VAX System Manager
Bristol-Myers Squibb, Princeton, New Jersey
Phone:  (609) 252-6144	Internet:  VENARD@BMS.COM
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