Autochanging tape drives used to be the stuff of science fiction among 3000 managers, but those days passed by before HP cut off making its Classic 3000 MPE V systems. Just because an autochanger is a standard storage option does not make it automatic to program, however.
A question posed to the community by systems manager John Pitman of RYCO Hydraulics reached for help on "programmatically controlling such autochangers -- to select a slot, and load the tape and come to ready." Advice is at hand, including a detour to a Looney Tunes classic. As it turned out, Pitman didn't need his programming, but the advice can make some autochangers toot smoother.
HP's pass-through SCSI driver came up in some advice. The software built by HP's labs and "not for the faint of heart" can assert a program's control over autochangers, although third party programs such as the Orbit Software Backup+/iX do this work. If you've never seen an autochanger at work, OpenMPE's Tracy Johnson pointed to great theme music, a tune called Powerhouse you will know as soon as you hear it, if you've ever watched a Warner Brothers cartoon.
As for being able to control the robot itself, you definitely need to have the [HP] SCSI pass-through driver configured and loaded, and then you need a program to actually issue the IOCTL calls to the robot with the properly formatted SCSI commands. There was such a program a long time ago from a vendor, but that's all gone now.
The pass-though driver is still available from HP for the strong hearted, a piece of coding designed to give 3000 sites control of SCSI devices HP didn't engineer or test for the server. Perhaps the high-test flutes and heavy octane horns of Powerhouse -- used in Duck Rogers and the 24th and a Half Century -- can be put up on the MP3 player while fitting the driver to MPE. ("Oh drat these computers -- they're so naughty and so complex," says Marvin the Martian in one installment. "I could just pinch them.")
Jack Connor of Abtech -- another OpenMPE volunteer -- pointed to similar complex answers about controlling DDS changers.
Typically, there's a second SCSI port/address assigned for the transport control which allows the selection of specific tape. For MPE, stacker mode is typically selected, which tells the drive to just mount the next tape in line when requested. I don't know if the DDS autoloaders have a network connection available like the C7145NA DLT autoloaders do; with that device's web interface you can reload any tape, bypass a bad tape, and so on.
Pitman checked in to report that a much simpler solution to his changer's control needs popped up. "On re-examining my code for HPDEVCONTROL, I found I had catered for 1- and 2-digit device numbers in the string passed, but I had configured the drive as dev 777. This produced a string dev number of 77, which doesn't exist as a tape drive. Once I fixed this, it works like a treat."
While that solves the control needs of HP autochangers at Ryco, the exercise also leaves the devices and the pass-through software with a classic piece of music by jazz master Raymond Scott as a theme song. It takes a community of 50-ish experts in an enterprise computer classic to connect long-ago-written, or long-gone, software with a tune that Warner Brothers' Carl Stalling used in a dozen 1950s cartoons.