MRIE behavior in SPC-2 vs SSC
relliott at hobbit.eng.hou.compaq.com
Fri Jun 4 13:58:37 PDT 1999
* From the T10 Reflector (t10 at symbios.com), posted by:
* relliott at hobbit.eng.hou.compaq.com (Robert Elliott)
There is a slight difference in the SPC-2 and SSC definitions of the
Method for Reporting Informational Exceptions (MRIE) bit in the
Informational Exceptions mode page 02h. (MMC-2 includes portions
of the SPC-2 description)
See SPC-2 revision 10 section 8.3.6 and SSC revision 17 section 184.108.40.206.
For MRIE = 4, for example, SPC-2 says:
This method instructs the device server to report informational
exception conditions, regardless of the value of the per bit of
the error recovery parameters mode page, by returning a
CHECK CONDITION status on any command.
This method instructs the device server to report information
exception conditions (regardless of the value of the per bit of
the error recovery parameters mode page) by returning a
CHECK CONDITION status on the next SCSI command (excluding Inquiry
and Request Sense) after an informational exception condition
There are two differences:
1. SSC exempts INQUIRY and REQUEST SENSE. SPC-2 does not. This
occurs for MRIE values 2, 3, 4, and 5.
The only other way to cause INQUIRY and REQUEST SENSE to return CHECK
CONDITION is to use a reserved bit. SSC's exemption seems appropriate.
2. SSC says the CHECK CONDITION will be returned on the next command.
SPC-2 says "any" command. This occurs for MRIE = 4 only.
In case of an actual hardware exception condition, you can't tell when
it happened so this doesn't matter. If the TEST bit is being used to
trigger a fake exception condition, however, the SSC requirement is
more useful since the command that must cause the CHECK CONDITION
can be predicted.
So, I have these questions:
1. Was this difference intentionally introduced?
2. Would the non-tape devices accept tightening the SPC-2 description
to match the new description in SSC? Do disk drives and other devices
already behave this way?
Rob Elliott UNIX mailto:relliott at hobbit.eng.hou.compaq.com
Houston, TX PC mailto:Robert.Elliott at compaq.com
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