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SCSI Commands

Quantum DLT 4000 Tape Drive 5-11

5.1.5 Unit Attention Condition

Queued Unit Attentions are implemented on the Quantum DLT 4000 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.

5.1.6 Behavior at Power-On and SCSI Bus Reset

The following apply to the DLT 4000 tape drive’s behavior at power-on and/or

SCSI bus reset:

• When the Quantum DLT 4000 is powered up, all device SCSI lines are set to

high impedance.

• The design of the DLT 4000 tape drive does not allow it to generate any

spurious signals on the SCSI bus at power-on.

• Within five seconds of power-on, and within 250 milliseconds (typically

under 4 milliseconds) after a SCSI bus reset, the DLT 4000 tape drive

responds to SCSI bus selections and returns appropriate, normal responses.

Tape motion commands will be returned with CHECK CONDITION status,

Sense Key Not Ready, until the tape medium has been made ready.

• The tape drive implements the hard bus reset option.

• The tape medium is rewound to Beginning of Tape (BOT).

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Quantum DLT 4000 Manual Página 111