Request Sense Handling of Deferred Errors

Knight, Frederick Frederick.Knight at
Tue Apr 12 06:09:41 PDT 2011

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NO.   This can be confusing, as there are 2 places where sense data is
returned.  One, is the autosense data that is associated with a command.
The second is the data buffer that is returned in response to the
>From the definition:
3.1.158 sense data: Data describing an error or exceptional condition
that a device server delivers to an application
client in the same I_T_L_Q nexus transaction (see 3.1.67) as the status
or as parameter data in response to
a REQUEST SENSE command (see 6.29). The format of sense data is defined
in 4.5.
The RED text is the first (autosense), the GREEN text is the second
(parameter data buffer) - notice the "OR" between the two types of sense
So, when there is a deferred error, and a REQUEST SENSE command is
received, the parameter data buffer that is returned will contain sense
data that describes the deferred error.  The autosense data associated
with the REQUEST SENSE command will be associated with the GOOD status
returned for the command itself.
Basically, a successful REQUEST SENSE command returns GOOD status (with
no autosense data); AND it returns a parameter data buffer that happens
to contain data that is in the format of sense data that describes the
event (deferred error in your example).
If the REQUEST SENSE command has a problem (an invalid field in the CDB
for example), then the command will return an error status with
autosense data that describes the problem with the command (INVALID
FIELD IN CDB).	In this case, there is NO parameter data buffer to be
returned, since the command failed.  This is what 6.29 describes.
		Fred Knight
From: Truong Nguyen - SISA [mailto:tru.nguyen at] 
Sent: Monday, April 11, 2011 11:33 PM
To: t10 at
Subject: Request Sense Handling of Deferred Errors
The Request Sense command definition in subclause 6.29 SPC4r30 states
that the "device server shall return Check Condition status for a
Request Sense command only to report exception conditions specific to
the Request Sense command itself".
Deferred errors may be indicated by returning Check Condition status as
defined in subclause 4.5.5 in SPC4r30.
In the event that the device server detects a deferred error condition,
and then subsequently receives a Request Sense command, should the
deferred error cause a Check Condition status to be returned for the
Request Sense command? It would seem not, but some clarification would
be appreciated.
Truong Nguyen
Samsung Information Systems America

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