Re: iSCSI : Digest Error Problems & CmdSN/ExpCmdSN window issues

[Santosh Rao <santoshr@cup.hp.com>]

Matt,

The description of CmdSN window mangement in Section 1.2.2.1 reads :

 "- The target MUST silently ignore any command
     outside this range or duplicates within the range not flagged with
     the retry bit (the X bit in the opcode)."

Does this imply :
- ignore all commands outside the (ExpCmdSN, MaxCmdSN) range.
- ignore all duplicate commands within the range that are not flagged with the
   retry
?

If so, a command with the "retry" bit set and received outside the
(ExpCmdSN, MaxCmdSN) window causes the target to drop the
received retry. Is this a valid interpretation of the draft ?

Regards,
Santosh

Matt Wakeley wrote:

> Santosh,
>
> I guess I don't understand what it is that you think needs clarification.
>
> -Matt
>
> Santosh Rao wrote:
> >
> > Matt,
> >
> > (You may want to take another look at the thread.). Here's the details again :
> >
> > > 3) The policy of "discard and restart" is also subject some race
> > > conditions in the CmdSN sliding window. At the time the digest error was
> > >
> > > detected at the initiator, the ExpCmdSN may not yet have acknowledged
> > > that
> > > command. This causes the initiator to restart the command with the same
> > > Initiator Task Tag, CmdSN and "retry" bit set.
> > >
> > > However, by the time the command gets to the target, the target may have
> > >
> > > updated its ExpCmdSN window having sent a later PDU which updated the
> > > ExpCmdSN. This results in the target discarding the received CmdSN since
> > >
> > > <js> at command restart you never really rely on the CmdSN. you will want
> > > to check
> > > the Initiator Task Tag and accept it in the above case. </js>
> >
> > The draft states the following on this subject :
> >
> > Section 5.1
> > =========
> > -    the initiator will reissue all outstanding commands with their
> >       original Initiator Task Tag and their original CmdRN if they
> >       are not acknowledged yet or a CmdRN of 0 (not-numbered) if they
> >       were acknowledged; the retry (X) flag in the command PDU will
> >       be set
> >
> > Section 1.2.2.1
> > ===========
> > - The target MUST silently ignore any command
> >    outside this range or duplicates within the range not flagged with
> >    the retry bit (the X bit in the opcode).
> >
> > This, to me, means :
> > - ignore all commands outside the (ExpCmdSN, MaxCmdSN) range.
> > - ignore all duplicate commands within the range that are not flagged with the
> > retry
> > bit. << "duplicate" added this time >>
> >
> > Can you please clarify the intent of the text ?
>
>
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