RE: iSCSI: Out Of Sequence due to null sequence with multiple con nections.

[Black_David@emc.com]

Sandeep,

> Still wading thru related emails but I believe that if a refCmdSN
> is added to the task management PDU (not present currently but
> could be added for task-related management commands), then it 
> might fix the above-mentioned flaws and allow for safe execution 
> and immediate delivery of the abort task to the target.  

I think this is a functional subset of Doug Otis's suggestion to always
use a CmdSN and add a header flag indicating that the command should
be executed immediately at the target rather than waiting for those with
prior CmdSNs to arrive.  Doug's suggestion also consumes less space
in the header.  As to (1) vs. (2):

> (1) The command takes effect immediately and its status/response
>         is available immediately.
> (2) The command affects all commands in flight, and its status/response
>        is delayed until all such effects are complete.

I think you've covered most of the ground in:

> 6) Task response can be returned as appropriate to conform with
>    SAM2 - either after in-flight commands arrive or immediately
>    since the target knows what needs to be done later.  I am slightly 
>    confused here since your goals (1)&(2) appear to be contradictory
>    for application to in-flight commands.. it depends on semantics 
>    what "taking effect" implies ?

IMHO, returning the response before task execution is complete
("the target knows what needs to be done later") not only does
not comply with SAM2, but can also yield rather unexpected
behavior (e.g., situations in which an in-flight command is aborted
significantly after the response to the abort command has been
returned to the Initiator).  If this is correct, goals (1) and (2) are
contradictory because there's only one response and achieving
both goals requires sending that one response at two different
times (not a good idea).  Hence the Initiator has to choose
between (1) and (2) for each task management command.

Thanks,
--David

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David L. Black, Senior Technologist
EMC Corporation, 42 South St., Hopkinton, MA  01748
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