Fw: FCP-2: Lost Write Data, Not Last Frame of Sequence, Unacknowledged classes.

Hugh Curley hcurley at indra.com
Fri Jun 28 14:05:30 PDT 2002


* From the T10 Reflector (t10 at t10.org), posted by:
* "Hugh Curley" <hcurley at indra.com>
*
Dave, Santosh,

Could you please send the response either to the reflector or to me
directly?  I am very interested in the answer, and I know several others who
are also.

Thanks,

Hugh


----- Original Message -----
From: "Santosh Rao" <santoshr at cup.hp.com>
To: "Dave Peterson" <dap at cisco.com>
Cc: "T10 Reflector" <t10 at t10.org>
Sent: Thursday, June 27, 2002 11:07
Subject: Re: FCP-2: Lost Write Data, Not Last Frame of Sequence,
Unacknowledged classes.


> * From the T10 Reflector (t10 at t10.org), posted by:
> * Santosh Rao <santoshr at cup.hp.com>
> *
> Howdy Dave,
>
> Thanks for the clarification. For the case of lost write data (class 3),
> where the target has the sequence initiative, Section 9.4.1 conflicts
> with Section 12.3.5.
>
> Section 9.4.1 must be modified to state that the target must not send a
> FCP_RSP when an exchange/sequence error is detected and it holds
> sequence initiative. This prevents targets from terminating commands
> with any possible sk/asc/ascq CHECK CONDITION which cannot be detected
> by the initiator, thereby, preventing the use of SLER.
>
> Is this change possible in FCP-2 ?
>
> Thanks,
> Santosh
>
>
> Dave Peterson wrote:
>
> > The statements refer to the actions to be taken by the initiator.
> > But, I don't know how FCP_DATA could be returned for a write operation
> > either.
> > The note is not correct and should be removed. I think the intent was to
> > specify the behavior for out-of-order class 3.
> >
> > > Since the last frame of the sequence is assumed to have made it to the
> > > target (lost write data iu was not the last frame of sequence), the
> > > target has the sequence initiative and can complete the exchange with
a
> > > FCP_RSP indicating a CHECK CONDITION status with appropriate
sk/asc/ascq
> > > (as per Section 9.4.1). In this case, is the initiator expected to
look
> > > for CHECK CONDITION command completions of certain sk/asc/ascq
> > > combinations and initiate a SLER operation on seeing those ? What
> > > specific sk/asc/ascq combinations should the initiator look for while
> > > parsing command completions to initiate SLER ?
> > >
> > > If this is not done, a write underrun condition as described above
> > > cannot be recovered from, since SLER will not kick in and the
> > > ULP/application will see the error.
>
> > For this case:
> >
> > The target may or may not have sequence initiative
> > (i.e., seq=1, seq_cnt=1 may not be the last frame of the sequence).
> >
> > For in-order delivery the target should have detected a Sequence error.
> >
> > Per clause 12.3.5 Additional error recovery by target:
> > For unacknowledged classes of service, the target shall not attempt
recovery
> > for Sequence errors. The target
> > shall depend on initiator time-outs for recovery.
> >
> > If SLER is enabled, the target should not return check condition.
> >
> > And we could use some words stating this in the doc...dap
>
> --
> The world is so fast that there are days when the person who says
> it can't be done is interrupted by the person who is doing it.
> ~ Anon
> *
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