User's Guide

Chapter 3 Emulated DLT7000 SCSI Commands
Overview of Command and Status Processing
118 Quantum DX-Series Software Interface Guide
Unit Attention
Condition
3
Queued Unit Attentions are implemented on the Quantum DLT7000 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.
Behavior at Power-
On and SCSI Bus
Reset
3
The following apply to the DLT7000 system tape drive’s behavior at
power-on and/or SCSI bus reset:
• When the Quantum DLT7000 system is powered up, all device SCSI
lines are set to high impedance.
• The design of the DLT7000 system 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 DLT7000
system 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).