Load Unload Command (1Bh) - Quantum DLT 8000 Product Manual

SCSI Commands
5.5

LOAD UNLOAD Command (1Bh)

The LOAD UNLOAD command tells the target to load or unload the tape media in
the tape cartridge. If no cartridge is in the tape drive, both LOAD and UNLOAD return
a CHECK CONDITION status with a NOT READY sense key set. Likewise, if the drive
has received an UNLOAD command with the Immediate bit set and then it receives
another command that would require tape motion or if it receives a TEST UNIT READY
command, the drive returns a CHECK CONDITION STATUS with a NOT READY
sense key set.
Operation of the UNLOAD version of this command is different if a media loader is
present.
Two modes of operation are possible if a media loader is configured. If none of the
media loader-specific commands have been issued, the device operates in the
sequential mode of operation described below. Once a media loader-specific
command has been issued, however, the sequential mode of operation (described
below) is disabled and the UNLOAD command becomes a NO OPERATION.
If the tape drive is in the default sequential mode of operation and an UNLOAD
command is received by the subsystem, the current cartridge is unloaded and
automatically moved to the magazine slot from which it was received. The cartridge
from the next magazine slot (if the slot is not empty) automatically moves from the
magazine into the drive, is loaded, and made ready. If the next magazine slot is empty,
no CHECK CONDITION status is created.
When the cartridge is unloaded into the last magazine slot, the subsystem does not
cycle back to slot 0. This prevents accidental overwriting of data when using a media
loader subsystem in sequential auto-loading mode. The next cartridge in the cycle
must be selected and loaded manually, or with a SCSI MOVE MEDIUM command.
The sequential loading feature of the loader can be enabled/disabled by modifying the
ENALDRAUTOLD and DISLDRAUTOLDMC parameters of EEPROM (mode page 3Eh of
the MODE SELECT command).
A media loader does not affect the tape drive's processing of the LOAD portion of the
LOAD UNLOAD command.
5-32
NOTE
Quantum DLT 8000 Tape System