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28 Using Special Features in Libraries
The ACI provides the following fundamental functions:
3
Coordinating the automation controller and the tape drive for Load and
Unload operations
3
Allowing the automation controller to retrieve information from the tape
drive
3
Setting tape drive configuration information
In addition, the following functions may be supported depending on the way
that the tape library is configured:
3
Providing upload and download of firmware images
3
Providing access to the contents of the Cartridge Memory
3
Providing a protocol for passing SCSI commands to the tape drive over
the interface
Note These notes refer to the “standard” automation drive variant.
Modes of Usage
There are three ways in which the drive can be used through ACI control:
Slave to a Library Controller
The ACI can receive commands such as Load and Unload from a specially
defined automation command set to control the action of the drive.
Most tape libraries need to be able to do this because they need to have close
control over any mechanical operations of the drive that could interfere with
the operation of the picker arm. For instance, in a soft load device such as an
Ultrium drive, the picker must let go of the cartridge at the exact moment that
the drive starts to pull it into the drive.
This degree of control over synchronization cannot be achieved though the
host’s backup software; it must be controlled directly by the library controller.
Most tape libraries work this way today. The process is transparent to the
backup software.
SCSI Pass-Through Mode
The ACI can receive “packetized” SCSI commands from an attached
controller and submit them to the tape drive as if they have been received on
the drive’s own SCSI bus. This enables the attached controller to access and
control the drive in exactly the same way as it would via the SCSI bus.