SAT TEST UNIT READY command translation

Douglas Gilbert dougg at
Thu Aug 11 03:30:56 PDT 2005

* From the T10 Reflector (t10 at, posted by:
* Douglas Gilbert <dougg at>
SAT revision 05, section 8.12.2 [Miscellaneous notes
(on the TEST UNIT READY command)] states:

"a) The TEST UNIT READY command is mapped to the Check
Power Mode ATA command. If the drive is in standby
power mode, then it is assumed that the drive is
incapable of accepting media access commands without
any intervention, so a CHECK CONDITION is returned with
the sense key set to NOT READY and the additional sense

However a (s)ATA disk in standby power mode will transition
to active power mode automatically when a media access
command is received (albeit with a delay while the disk
spins up). A SCSI disk reacts the same way when it is
in standby mode. That additional sense code above is
appropriate when a SCSI disk is in stopped power state
(a state not defined for ATA disks). SAT translates
a START STOP UNIT (start=0) SCSI command to the Standby
ATA command (while the same SCSI command would put a
SCSI disk into stopped power state).
So is 8.12.2 miscellaneous note a) correct?

Alternatively SAT could define its REQUEST SENSE to yield
power condition information (as per SPC-3 rev 23).

Doug Gilbert

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