RFID (request for implementation description): SBC-4 Remove Unused MMC Restrictions (T10/14-238r0)

Elliott, Robert (Server Storage) Elliott at hp.com
Mon Sep 15 17:27:36 PDT 2014

* From the T10 Reflector (t10 at t10.org), posted by:
* "Elliott, Robert (Server Storage)" <Elliott at hp.com>
> * From the T10 Reflector (t10 at t10.org), posted by:
> * Paul Suhler <Paul.Suhler at hgst.com>
> I created a proposal for SBC-4 to clean up the "Restricted for MMC-6" bits
> that we found yesterday in six commands that have never appeared in any MMC
> standard:
>    http://www.t10.org/cgi-bin/ac.pl?t=d&f=14-238r0.pdf
> I'd like to make a more precise request in regards to this proposal:	Does
> anyone know of any MMC device that sets the restricted bit in any of the
> following commands:
> READ(16) byte 14 bit 7
> VERIFY(12) byte 10 bit 7
> VERIFY(16) byte 14 bit 7
> WRITE(16) byte 14 bit 7
> WRITE AND VERIFY(12) byte 10 bit 7
> WRITE AND VERIFY(16) byte 14 bit 7
Those were requested by Keiji Katata, Pioneer and the MMC working 
group and first went into sbc2r09 (see CAP minutes 03-047).  
>From my notes at the time...
"MMC has assigned those bits in the CD/DVD command set to support
streaming.  This means:
* on reads, if a bad block is encountered, just return zeros
  and proceed to the next block
* on writes, if a bad block is encountered, just skip it and
  proceed to the next block
This is done on a per-command basis.  It lets multimedia software use:
* non-streaming accesses when accessing important data like
  file directories, firmware, etc. where data integrity is important
* streaming accesses when accessing files containing audio/video data
  streams where performance matters more than integrity
This is very useful for DVD players, DVD recorders, PVRs like
ReplayTV and Tivo, etc.  It could be useful for large video servers
as well.
Keiji Katata from Pioneer suggested that SCSI disk drives might
want to implement the same features.  T13 has been adding streaming
support to the ATA command set in ATA/ATAPI-7.
The bits used in MMC-4 for the features will be marked as
"restricted" in SBC-2 so they don't get used for some other purpose.
Since optical drive capacity lagged magnetic drive capacity, MMC
never added 16-byte CDBs; most ATAPI silicon doesn't support
that packet size. They never picked up VERIFY (12) and WRITE 
AND VERIFY (12) to support > 64 Ki block transfer sizes in one 
command, either.  Nobody has proposed adding the Streaming bits
to the SBC commands (a few similar proposals have been discussed,
but they always want something more complex), so they've just sat
as restricted for 11 years.
Rob Elliott    HP Server Storage
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