Quantum Instruments DLT 7000 - Manual (Page 90)

SCSI Description
3-26 Quantum DLT 7000 Tape System
• The tape medium is rewound to Beginning of Partition (BOP, i.e.,
Beginning of Tape [BOT]).
Note that the tape drive does not implement the hard reset alternative for bus
RESET processing.
The tape drive recognizes multiple bus resets in succession as well as bus resets
of arbitrarily long duration (powering on conditions). It recovers within the time
limits specified above following the last bus reset.
3.6.3 Queued Unit Attentions
Queued Unit Attentions are implemented on the tape drive and are maintained
separately for each valid LUN for each initiator. Unit Attentions are created as a
result of the following circumstances:
• Power on
• Bus reset
• Bus device reset message
• When the media may have changed asynchronously
• When another initiator has changed the mode parameters
• When a firmware (microcode) update has completed
Two (2) queued Unit Attentions are not unusual. For example, if a drive is
powered up and a cartridge is loaded, “power up” and “not ready to ready
transition” Unit Attention messages are created. Due to a limited number of
Unit Attention buffers, if an initiator does not clear Unit Attentions queued for
it, the tape drive at some point stops generating new Unit Attention messages
for the Initiator-Logical Unit (I-L) combination (existing messages remain
queued).
A LOAD command does not generate a Unit Attention message for the initiator
that issued the command, since the transition to ready is synchronous.