Command Deadlines: HP's Modest Proposal

Paul Suhler Paul.Suhler at hgst.com
Wed Sep 3 14:30:44 PDT 2014


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Hi, all.
Curtis Ballard has made an interesting suggestion for a major change to last
week's T10/14-107r2:
Instead of providing two sets of fifteen timeouts, one timeout would be
provided per-opcode-per-I_T_L nexus.  That timeout would be used if a
newly-allocated bit in the CDB's Control byte were set.
Advantage:
No need to wait for the Command Priority attribute to be added to transport
implementations and to driver stacks, which could take years.
Disadvantage:
In cases where an initiator wants to change the timeout for  a particular
command (e.g., READ(16)) on a particular LU, it would have to send a MODE
SELECT.
Questions:
1)	Does anyone feel that one timeout per opcode per I_T_L nexus is too
much of a constraint?  HP doesn't.
2)	Does anyone object to using mode pages, with the requirement that the
data length on MODE SELECT must match the data length on MODE SENSE?  (The
alternative is yet another command.)
Thanks for your feedback,
Paul
Paul A. Suhler, PhD
Research Staff Member
HGST Research
paul.suhler at hgst.com
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