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Pat
The problem is that some implementations (drivers and sometimes
hardware) limit the size of the CDB's they process to 12 bytes. This is too
small to send a 48-bit LBA command. That is the only reason for defining
the 12 byte CDB.
------------------------------------------------
Curtis E. Stevens
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Why did the chicken cross the road? Colonel Sanders: You mean I missed one?
-----Original Message-----
From: Pat LaVarre [mailto:[EMAIL PROTECTED]
Sent: Friday, October 29, 2004 9:20 AM
To: Curtis Stevens
Cc: Sheffield, Robert L; Andy Warner; [EMAIL PROTECTED]
Subject: Re: [t13] RE: comment on T10 ATA-passthru
> I think we are in agreement.
Me too.
> I would like to discuss the direction at the CAP meeting. From my
> perspective, it is not a big deal to encode the direction as a part of
> the opcode. However, I am a bit concerned because we could end up
> burning 6 opcodes for this capability (12/16 byte CDB IN/Out/Non data
> transfer).
To fit the SCSI tradition of deciding direction by op, we could burn just 2
ops, and leave the ATA-specific distinctions to appear inside the CDB. For
example, we could say that an expected length of 0 means non data transfer
protocol, no matter if it appears in combination with the SCSI ATA In op or
the Out op.
If we only sometimes need more than 12 bytes of CDB, then we sometimes do,
and if we want the compatibility of also defining a 12 byte rather than 16
byte CDB, then the cost rises to 4 ops rather than 2, yes. But I've missed
the argument for needing to burn 6 ops.
Perhaps we should ask the t10 at t10.org folk to comment on the continuing
significance of the decide direction by op tradition.
Pat LaVarre
