Request Sense DESC bit, minor conflict between MMC-6 and SPC-4

Mike Berhan mikeb at
Tue Apr 21 15:52:13 PDT 2009

* From the T10 Reflector (t10 at, posted by:
* "Mike Berhan" <mikeb at>
The MMC specification refers one to SPC-3 for the Request Sense CDB
definition.  It states this regarding the DESC bit in the CDB:
"Since MM Drives support only a 32-bit LBA format, MM Drives ignore the
setting of the Desc bit in the
REQUEST SENSE command CDB and return only fixed format sense data.
SPC-3 does not seem to be specific (unless I've missed it) on what the drive
should do if it doesn't support Descriptor format sense data but receives a
DESC=1 request.  However, SPC-4 is very clear on this in Table 251 (DESC
bit).  It states:
"The device server shall return no parameter data and terminate the REQUEST
SENSE command with CHECK CONDITION status with the sense key set to ILLEGAL
REQUEST and the additional sense code set to INVALID FIELD IN CDB."
A quick test of the optical drives I have attached show that they do ignore
the DESC bit thereby meeting the MMC requirement but contradicting the SPC
requirement.  This is a minor issue as I suspect no optical software (other
than test software) issues a Request Sense with the DESC bit set.  It is a
conflict between MMC-6 and SPC-4 that I don't believe has been mentioned
It seems to me that MMC-6 should adopt what SPC-4 has defined but I'll leave
that to the two committees if they're interested in addressing this.
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