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Queued Unit Attentions are implemented on the Tandberg DLT8000 tape drive
and are maintained separately for each valid LUN for each initiator. Unit
Attentions are created in each of the following circumstances:
• At Power On
• At Bus Reset
• At Bus Device Reset message
• When the medium may have changed asynchronously
• When another initiator changes the Mode Parameters
• When a firmware (microcode) update has completed
Two queued Unit Attentions are not unusual. For example, if a unit is powered up
and a tape cartridge is loaded, Power Up and Not-Ready to Ready Transition Unit
Attentions are created. Due to the limited number of Unit Attention buffers, if an
initiator does not clear Unit Attentions queued for it, at some point the tape drive
stops generating new Unit Attentions for that initiator-logical unit combination
(existing ones will be left queued, however).
A LOAD command does not generate a Unit Attention for the initiator that issued
the command since the transition to Ready is synchronous.