Behavior of TEST UNIT READY command in idle and standby power conditions

Kevin_Marks at Kevin_Marks at
Tue Nov 27 13:40:02 PST 2012

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Not sure I agree Gerry.
The description in the TUR command says "If the logical unit is able to
accept an appropriate medium-access command without
returning CHECK CONDITION status, this command shall return a GOOD status. If
the logical unit is unable to become operational or is in a state such that
an application client action (e.g., START UNIT command) is required to make
the logical unit ready, the command shall be terminated with CHECK CONDITION
status, with the sense key set to NOT READY."
The only defined states where this is not the case is Stopped state or any
_wait state coming from stopped (and that was a legacy behavior).
It's all in the state machines.
From: owner-t10 at [mailto:owner-t10 at] On Behalf Of Gerry Houlder
Sent: Tuesday, November 27, 2012 9:27 AM
To: T10 Reflector
Subject: Behavior of TEST UNIT READY command in idle and standby power
Some questions have come up about the behavior of TEST UNIT READY command
when the target is in an idle or standby power condition.
One opinion is that TUR should be treated as a command that can be processed
in idle and standby power conditions, so therefore should complete with GOOD
Another opinion is that TUR should respond with CHECK CONDITION status with
sense bytes indicating the target is in a low power condition and the target
should not attempt  to change to a higher power condition. (Read or write
commands would trigger the target to change to active power condition, so TUR
action would be different). The advantage of this behavior is that it could
be used to poll for low power conditions in lieu of using REQUEST SENSE
The existing description of TUR command in SPC-4 rev. 36e doesn't address the
expected behavior for this case, other than the table of "preferred TUR
responses" doesn't include any of the low power condition sense combinations.
However, folks can argue that there are a lot of other combinations that are
not included there but should be reported if the conditions are present.
I would like to see responses on the reflector for the preferred behavior of
TUR when in a low power condition. If there is a convergence of opinion, i
would like to have that opinion reflected in description of the TEST UNIT
READY command to avoid having to readdress this issue in the future.

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