Proposal to add a new modifier to SCSI Write commands.

Jeff Blaalid, CMD Technology, (714) 470-3155 BLAALID at
Mon Dec 2 13:06:49 PST 1996

* From the SCSI Reflector (scsi at, posted by:
* "Jeff Blaalid, CMD Technology, (714) 470-3155" <BLAALID at>

    The real problem with the proposal is that is attempting to solve
    a very specific and narrow scoped problem.

    The real goal should be to:

            "Mark the block indicating 'reactive data', thus generating 
             a CHECK CONDITION when read".

            The purpose is to provide initiators the ability to 
            mark blocks without having to interfere with the data payload
            or ecc areas.

    This has two benefits:

            1)  Allows the O.S. vendors to actually place "important"
                data in the block and does not limit the use of this feature
                to Digital's Forced Error situation.

            2)  Doesn't mess around with ECC issues.  Leaves the marking
                of the block up to the drive vendors.  Hopefully
                placing this bit in the header/edc area instead of 
                the ecc section.

    My version of the proposal would be:

        A new WRITE command (or bit in the exiting WRITE commands) that
        marks the block as "reactive data'.  The drive shall take the
        1 block of data, write it, and mark it as "reactive data".

        The drive is free to implement this command in any convenient way,
        provided that all subsequent reads result in a "Check Condition"
        with a new ASC/ASCQ pointing to the block that contains the
        "reactive data" that was earlier written.

 | Jeffrey S. Blaalid       | CMD Technology, Inc. | Tel: (714) 470-3155  |
 | Dir, Digital Product Dev.| 1 Vanderbilt         |      (800) 426-3832  |
 | Email: blaalid at   | Irvine, CA  92718    | Fax: (714) 455-9554  |
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