00-212r0 -- Beyond Beyond 2TB

Ralph Weber ralphoweber at CompuServe.COM
Tue Apr 18 13:23:35 PDT 2000

* From the T10 Reflector (t10 at t10.org), posted by:
* Ralph Weber <ralphoweber at compuserve.com>
A proposal for consideration at the May meetings has
been placed on the T10 FTP site as:

< ftp://ftp.t10.org/t10/document.00/00-212r0.pdf >

The proposal contains tables and other features that cannot be
translated to ASCII for reflector distribution.  You will need
to download the PDF to review the proposal.

The proposal can be summarized as follows:

Doc:  T10/00-212r0
Date: 18 April 2000
To:   T10 Technical Committee
From: Ralph Weber
Subj: Beyond Beyond 2TB

The handling of mode page block descriptors in 99-259r4 is not
backward compatible with old host driver software.

The presence of LONGLBA=1 in the mode page header returned by a MODE
SENSE(10) command is intended to inform that application client that
the block descriptors are in the 16-byte format instead of the 8-byte
format that has applied to MODE SENSE(10) commands since SCSI-2.
However, the LONGLBA bit is a new definition, introduced by 99-259r4.

Old host driver software will not be inspecting the LONGLBA bit,
because the bit was not defined in SCSI-2 or any SPC version prior to
SPC-2 revision 16. Instead, old host driver will process every
16-byte block descriptor as if it were two 8-byte block descriptors.

This proposal adds further controls on the use of LONGLBA to insure
that host driver software does not see LONGLBA=1 unless it is
prepared to deal with it.

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