SCSI-3 Block Commands

Jeff Williams jlw at
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.

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

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