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

Sam.Pappal at Sam.Pappal at
Wed Dec 8 16:00:46 PST 2010

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Some legacy hosts currently in wide use and perhaps some drivers try
Read 6 during boot and operation as part of failure recovery. These
hosts will hang there and may require reboot if Read 6 is not supported
by the drive. ..  can become a deadly embrace in my experience. 
Systems Engineering Staff 
From: owner-t10 at [mailto:owner-t10 at] On Behalf Of Matthew
Sent: Wednesday, December 08, 2010 6:28 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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