Technical information

HGST Ultrastar C15K600 Hard Disk Drive Specification
302
20.1.5
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 LUN Reset Task Management function or Hard Reset
sequence. In all of these cases, a unit attention condition is generated for each initiator.
- 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 command. 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.
- The unit attention condition persists for each initiator until that initiator clears the condition from the logical unit
as described below. Several commands are handled as special cases during a unit attention condition these
cases are also discussed below.