READ (6), WRITE (6), et al.

Curtis Stevens curtis.stevens at
Fri Dec 10 08:47:41 PST 2010

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Matthew, the issue here is making commands mandatory that make no real sense
to use.  READ (6) has the capability to read approximately 512 MiB at the
front of the media.  This is meaningless in a device that supports 1 million
times that.  There is development and support costs in continuing to require
commands that were used in 1984 but have no real application for today.
Obsoleting the command does not prevent devices from supporting them, but it
does send a stronger message to host system developers that they should
modernize their systems.
Curtis E. Stevens
Sr. Staff  Engr - Standards & Features Technology
20511 Lake Forest Drive #A 113-F
Lake Forest, California 92630
Phone: 949-672-7933
Cell: 949-307-5050
E-Mail: Curtis.Stevens at  
From: owner-t10 at [mailto:owner-t10 at] On Behalf Of Matthew
Sent: Wednesday, December 08, 2010 3:28 PM
To: Mark Evans
Cc: t10 at
Subject: Re: READ (6), WRITE (6), et al.
I see no real advantage in obsoleting commands that have been well known
since 1984 *and* remain in active use today. For the random few people still
booting microVaxen, or even SparcStation 1 (I know someone who still uses
one as a desktop system), why shouldn't the be able to use modern (through
appropriate electrical dongles) storage?
Will drive vendors *really* reap *substantial* cost savings with this?
As capacities in storage devices have increased, there has been much
discussion about how several commands do not have the capability to access
or reflect the new capacities.	For example, READ (6), READ (10), READ (12),
WRITE (6), WRITE (10), WRITE (12), and several other commands can not
address LBAs for storage devices having capacities greater than about 2.2
TB, but there are devices today exceeding this capacity and the trend only
goes up and to the right.  In addition, READ (6) and READ (10) are currently
mandatory commands in SBC-3.  There is even a note in the table listing the
commands that reads, "Application clients should migrate from the READ (6)
command to the READ (10) command and from the WRITE (6) command to the WRITE
(10) command."
I think that, at the very least we should make READ (6) and READ (10)
optional and replace the note with, "Application clients should migrate from
the READ (6), READ (10), and READ (12) commands to the READ (16) command and
|from the WRITE (6), WRITE (10), and WRITE (12) command to the WRITE (16)
command."  I go so far as recommending that all commands incapable of
dealing with greater than 2.2 TB be made obsolete, though I could see
waiting to do this until SBC-4.  Thoughts?  Comments?
Please feel free to call or send an email to me with any comments or
questions that you have about this stuff.
Mark Evans
Western Digital Corporation
5863 Rue Ferrari
San Jose, CA 95138
Email: mark.evans at  

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