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Chapter 4 SCSI Interface

General SCSI Bus Operation

62 Quantum|ATL PowerStor L500 Series Tape Library User’s Guide

Disconnects from the SCSI bus are done on operations that take

significant amounts of time such as Move Media commands. This

allows other devices to access the bus. This disconnecting is

configurable by use of the Disconnect-Reconnect Mode Parameters

page.

Initiator/Target

Operation

The library does not act as an initiator on the SCSI bus. Therefore,

the device does not:

• Generate unsolicited interrupts to the host

• Initiate its own SCSI commands

• Assert bus reset

SCSI IDs and

Logical Unit

Numbers (LUNs)

The library has one logical unit. The library always appears as

LUN 0.

If the LUN specified in the Identify message is invalid, the library

accepts the Command Descriptor Block (CDB). Unsupported

LUNS are handled in one of three ways:

• If the command is Inquiry, the target returns the Inquiry data

with the peripheral qualifier set to 011, indicating that the

target does not support the LUN in question.

• If the command is Request Sense, the target returns sense data.

The sense key is Illegal Request with an additional sense code

of Invalid Logical Unit Number.

• For any other command, the target terminates the Check

Condition status, and generates the above sense data.

Unit Attention

Condition

Queued Unit Attentions are implemented on this device, and are

maintained separately for each Initiator. Unit Attentions are

created in the following circumstances:

• Power on

• Bus reset

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Quantum L500 Guia do Utilizador Página 76