MRIE behavior in SPC-2 vs SSC

[gop at us.ibm.com]

* From the T10 Reflector (t10 at symbios.com), posted by:
* gop at us.ibm.com
*
Rob,
I do not believe requiring the recovered error to occur on the 'next SCSI
command' is a behavior we want. It should state 'any command' as is the case in
the current SPC-2. The reason for this is that we will only report a 'recovered
error' on commands that the initiator would normally expect to see a 'recovered
error' (e.g., reads and writes) and that type of command may not be the 'next'
command.

The same problem is in the definition on MRIE=3 in SSC.

In general I am uneasy about the way these descriptions have changed (i.e.,
putting text in ( )) but not enough to make comments on.

Bye for now,
George Penokie

Dept PPV  114-2 N212
E-Mail:    gop at us.ibm.com
Internal:  553-5208
External: 507-253-5208   FAX: 507-253-2880




relliott at hobbit.eng.hou.compaq.com (Robert Elliott) on 06/04/99 03:58:37 PM

To:   t10 at Symbios.COM
cc:    (bcc: George Penokie/Rochester/IBM)
Subject:  MRIE behavior in SPC-2 vs SSC





* 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 5.3.4.6.

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.

SSC says:
  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
  was detected.


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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