SCSI-3 Block Commands

Jeff Williams jlw at hpbs1506.boi.hp.com
Mon Aug 1 09:47:31 PDT 1994



> Hi there. My name is Thomas "Rick" Tewell and I am currently editing
> the SCSI-3 Block Commands document. I have a few questions for the
> committee/reflector.

First, thanks for volunteering!


> 2. Should there be any verbage describing suggested action to be
> taken when optional bit(s) are set in the CDB of a mandatory command?

For example???  I think that all of the actions for options are 
currently defined.  I don't know of any bits where the actions are
not specifically called out.  The implementations may vary, but 
the top level definitions exist.


> 3. Is there any interest in adding a definition for an optional
> Scatter Write/Gathered Read command to speed up the access of
> 'logically tied' blocks of data on a device that might be physically
> disjoint on the media. This would allow for very quick reading and
> writing of fragmented files on the disk.

No!  The time required is not significantly smaller.  If I have to 
process three reads from different locations, the total time is dominated
by the seeks and not the command processing.  In addition, you would
have to define a parameter block for the gather which could not be
sent in the same command as the data returned since SCSI does not
allow bi-directional data on one command.  This gets real messy.

You may want to make a proposal and bring it to the committee, but you
cannot just add it into the document as the editor.  This restriction
should be true for all technical changes.


Regards,
Jeff
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Jeffrey L. Williams                                HP TelNet: 396-5030
Disk Controllers Lab             	 Telephone: (1) (208) 396-5030
Disk Memory Division                     Facsimile: (1) (208) 396-6858
Hewlett-Packard Co.                    ARPANET: jlw at hpdmd48.boi.hp.com
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