When should Mode parameter header (not) be returned?

Eric Agan eric at elegantinvention.com
Wed Aug 15 00:40:07 PDT 2012

* From the T10 Reflector (t10 at t10.org), posted by:
* Eric Agan <eric at elegantinvention.com>
Should Mode Sense(6) and Mode Sense(10) return the appropriate Mode
parameter header even if an unsupported Page or Subpage was requested?
SPC-3 states:
"An application client may request any one or all of the supported
mode pages from the device server. If an application
client issues a MODE SENSE command with a page code or subpage code
value not implemented by the
logical unit, the command shall be terminated with CHECK CONDITION
status, with the sense key set to ILLEGAL
REQUEST, and the additional sense code set to INVALID FIELD IN CDB."
...but doesn't seem to clarify whether the header should be returned
anyway or not.
What about other errors such as requesting Changeable Values when the
logic unit doesn't implement them? SPC-3 dictates the same response as
above for that scenario.
My assumption has been to always return the header.
Eric Agan
Elegant Invention
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