User's Guide

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
4
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)
4
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
4
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