Quantum 10K II - Manual (Page 78)

SCSI Description
Quantum Atlas 10K II Ultra160/m SCSI Hard Disk Drives 5–11
5.4 Auto Contingent Allegiance Condition and Contingent Allegiance
Condition
Auto Contingent Allegiance condition (ACA) is the SCSI-3 term for the condition of
the drive immediately after it returns a CHECK CONDITION status code. While it
is in this condition, the drive:
•
Keeps the status information (sense data) that characterizes the nature of, and
the reason for, the command's failure.
• Suspends execution of all commands that were queued behind the command
that failed (includes commands from all initiators, tagged or untagged).
• Discards and returns BUSY status for both tagged and untagged drive access
commands from other initiators.
The Auto Contingent Allegiance condition remains in effect until cleared by one
of the following:
•
TARGET RESET message received from any initiator
• ABORT TASK SET message received from the allegianced initiator
• Subsequent command received from the allegianced initiator
After receipt of an ABORT TASK SET message from the “allegianced” initiator, the
drive clears any queued command sourced by that initiator and processes the
remaining queued commands.
For Parallel SCSI, as its first action following receipt of the CHECK CONDITION
status code, the initiator sends a REQUEST SENSE command to retrieve the sense
data. Any other command from the initiator causes the drive to set the sense key to
NO SENSE and the additional sense code to NO ADDITIONAL SENSE
INFORMATION. These actions happen prior to resuming execution of queued
commands, or, if there are no commands queued, before processing a new command.
Also for Parallel SCSI, after receipt of the REQUEST SENSE command or any other
command from the “allegianced” initiator, the drive resumes processing of the
queued commands in the normal manner if the QErr bit in the MODE SELECT
Control Mode page is set to 0, its default value. If the value of QErr is 1, the drive
aborts all queued commands and generates a Unit Attention condition for initiators
with commands in the queue. A Unit Attention condition is not generated for the
“allegianced” initiator if commands belonging to it are flushed from the queue.