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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