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21.6.5 Unit Attention Condition
The target generates a unit attention condition when one of the following occurs:
•
The target has been reset
This includes a power-on reset or a reset caused by a Target Reset Task Management function or Reset LIP. In all of
these cases, a unit attention condition is generated for each initiator. In addition, a process login (PRLI) will cause a
Unit Attention Condition Power-On Reset for that initiator with an Additional Sense Code and Additional Sense
Code Qualifier reported as Power-On Reset, Power-On Reset Occurred.
•
MODE SELECT command has been executed
In this case, a unit attention condition is generated for all initiators except the one that issued the MODE SELECT
command. The Additional Sense Code and Additional Sense Code Qualifier reported is MODE PARAMETERS
CHANGED. The unit attention condition is generated if any of the current page parameters are set by the MODE
SELECT command. The target does not check to see that the old parameters are different from the new parameters.
For example: If the initiator issues a MODE SENSE command with a page code to report the current values followed
by a MODE SELECT command with the same parameter list, a unit attention condition is generated despite the fact
that the current parameters were not changed from their previous value. However, if the target detects an illegal
parameter or error condition prior to modifying the current parameters, a unit attention condition is not generated
since the parameters were not set. The unit attention condition is also not generated if the MODE SELECT command
parameter list does not include any pages and only the header or header/block descriptor is present.
•
FORMAT UNIT command has been executed
In this case, a unit attention condition is generated for all initiators except the one that issued the FORMAT UNIT
command. The Additional Sense Code and Additional Sense Code Qualifier reported is NOT READY TO READY
TRANSITION, (MEDIUM MAY HAVE CHANGED). This indicates that the block descriptor parameters from the
last MODE SELECT command have been used and are now considered current values.
•
WRITE BUFFER command to download microcode has been executed
In this case, a unit attention condition is generated for all initiators except the one that issued the WRITE BUFFER
command. The Additional Sense Code and Additional Sense Code Qualifier reported is MICROCODE HAS BEEN
CHANGED.
•
Commands Cleared by another initiator
This unit attention condition is generated after an initiator sends a Clear Task Set Task Management function. The
unit attention condition is generated for all other initiators with I/O processes that were either active or queued for the
logical unit. The Additional Sense Code and Additional Sense Code Qualifier reported is COMMANDS CLEARED
BY ANOTHER INITIATOR.
•
LOG SELECT command with PCR bit has cleared parameters.
In this case, a unit attention condition is generated for all initiators except the one that issued the LOG SELECT com
mand. The additional sense code and additional sense code qualifier reported is Log Select Parameters Changed.
•
The registration or reservation made by a Persistent Reserve Out command was cleared by another initiator.
In this case, a unit attention condition is generated for the initiator that held the cleared registration or reservation.
•
A Predictive Failure Analysis threshold has been reached and the Method of Reporting field of mode page 1Ch is 2h.
Hitachi Ultrastar 15K450 (FC-AL) Hard Disk Drive Specification
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