Re: iSCSI: plugfest4 issues

["Julian Satran" <Julian_Satran@il.ibm.com>]

Santosh,

I may change the words - thanks - but that will not solve the issue raised - that is when are the bits set in relation to the status.

Julo

Santosh Rao <santoshr@cup.hp.com> Sent by: santoshr@hpcuhe.cup.hp.com 08/01/2002 08:11 PM

To:        Julian Satran/Haifa/IBM@IBMIL         cc:        IPS Reflector <ips@ece.cmu.edu>, Robert Snively <rsnively@brocade.com>         Subject:        Re: iSCSI: plugfest4 issues

Julian,

I agree with you that the wording should be sufficient as called out in
Section 9.4 description of the bits and the resid field.

However, in observance of the fact that non-interopability has been
noticed in this area, it may help to tighten the wording for the
description of the o/O and u/U bits in the "SCSI Response" description
in Section 9.4. Perhaps, the use of "MUST" directive when calling out
the condition for the u/U/o/O bits to be set would help.

Also, In Section 9.4.4, instead of :
"The Residual Count field is only valid in the case where either the U
bit or the O bit is set."

I suggest :
"The Residual Count field MUST be valid when either the U or the O bit
is set".

Similar wording for the Bi-di read residual count.

Thanks,
Santosh


Julian Satran wrote:
> 
> Santosh,
> 
> I think that this behaviour should be specified by SPC3. I looked
> (again) into the FCP docs and like iSCSI they do not say anything
> beyond
> iSCSI says. Like iSCSI they specify that the field is valid when the
> Oo/Uu bits are set but nothing about how those bits relate to status.
> SPC says nothing about that either  (beyond that the bits set are not
> necessarily an indication of error).
> 
> Julo
> 
>  Santosh Rao
>  <santoshr@cup.hp.com>                     To:        IPS Reflector
>  Sent by:                          <ips@ece.cmu.edu>, Julian
>  santoshr@hpcuhe.cup.hp.com        Satran/Haifa/IBM@IBMIL,
>                                    rdr@io.iol.unh.edu
>  08/01/2002 03:44 AM                       cc:        Robert Snively
>                                    <rsnively@brocade.com>, T10
>                                    Reflector <t10@t10.org>
>                                            Subject:        Re: iSCSI:
>                                    plugfest4 issues
> 
> 
> 
> Julian & Robert [Russell],
> 
> I raised the same query regarding RESID for FCP/FCP-2 this time last
> year. The response I got for FCP/FCP-2 was that RESID information
> shall
> be valid, regardless of the scsi status returned. The RESID field, can
> be checked by the scsi transport drivers independent of the SCSI
> STATUS.
> 
> I have enclosed the T10 response from Rob Snivelly below on that
> issue.
> As per FC-PLDA, the RESID information is valid, regardless of the scsi
> status returned by the device.
> 
> An example of this is the case of "NO SENSE" or "RECOVERED ERROR"
> check
> condition, when the data transfer may have taken place and a CHECK
> CONDITION is returned. Also, for other CHECK CONDITION status',
> partial
> data transfer may have taken place and hence, resid information should
> be present.
> 
> It would be good to maintain consistent behaviour across the scsi
> transports in this regard, since protocol bridging from iscsi to FCP
> domain would expect RESID information in the FCP domain, regardless of
> scsi status.
> 
> This also allows scsi transports to remain free of SCSI command set
> details. (ex : the scsi transport drivers do not need to parse for
> CHECK
> CONDITION or GOO status information.)
> 
> Thanks,
> Santosh
> 
> -------------------------------------------------------------------------
> 
> Subject: Re: iSCSI: plugfest4 issues
> Date:    Thu, 1 Aug 2002 02:52:19 +0300
> From:   "Julian Satran" <Julian_Satran@il.ibm.com>
> To:     "Robert D. Russell" <rdr@io.iol.unh.edu>
> CC:     ips@ece.cmu.edu
> 
> Bob,
> 
> Thanks - some comments in text. Julo
> 
>  "Robert D. Russell" <rdr@io.iol.unh.edu>
> 
> Julian:
> 
> Four issues came up today at the iSCSI plugfest:
> 
> 1. A question about whether or not the Residual Count field and the
>  appropriate O and U bits need to be computed on all SCSI Response
>  PDUs, regardless of the values in the Status and/or Response fields.
> 
>  One point of view says that the Residual Count field and the O and U
>  bits appear to be strictly iSCSI values that are derived by the
>  iSCSI target layer from the ExpectedDataTransferLength field of the
>  SCSI Command PDU and the DataSegmentLength fields of the DataIn or
>  DataOut PDUs sent as part of this command.  Therefore ,the iSCSI
>  target always computes a Residual Count value without regard to the
>  Status and/or Response fields, since these are SCSI values.
> 
>  The other point of view says that the Residual Count field, and the
>  O and U bits, need only be set when the Status and Response fields
>  indicate that the command was completed at the target with a GOOD
>  Status, and the target does not have to compute or set the Residual
>  Count field and the O or U bits for other values of the Status and/or
>  Response fields.
> 
>  Which is it?  In any case, could this be clarified somewhere in the
>  standard, most likely in section 9.4.4.
> 
> +++ Residual count fields are in fact carrioed over from the SCSI
> layer.
> I know that none of the SCSI docs specifies
> exactly their behavior and it strikes me as a bad idea to have
> protocols
> specify them.
> The values should be valid any time the target decides to put them in.
> 
> +++
> 
> -------------------------------------------------------------------------
> Subject: RE: FCP_RSP Residual Checking.
> Date:    Thu, 5 Jul 2001 13:18:42 -0700
> From:    Robert Snively <rsnively@brocade.com>
> To:      "'Santosh Rao'" <santoshr@cup.hp.com>,
>         T10 Reflector <t10@t10.org>,
>         Fibre Channel T11 reflector <fc@network.com>
> 
> Robert Snively wrote:
> >
> > >  Is the target required to initialize the fields FCP_RESID_UNDER,
> > >  FCP_RESID_OVER & FCP_RESID when any I/O is completed
> > >  without the data phase having transferred exactly
> > >  FCP_DL bytes, regardless of the SCSI Status being returned ?
> >
> > >  When the target generates a CHECK CONDITION on an I/O
> > >  and may have returned less than FCP_DL bytes in the data
> > >  phase for that I/O, is it
> > >  required to set the FCP_RESID_UNDER to 1 and indicate the number
> of
> > >  bytes not transferred in the FCP_RESID field?
> >
> > The intent is that the answer to your second question is:
> > FCP_RESID should appropriately regardless of the SCSI Status
> > being returned.  The classic errors of that class are those
> > involving successful completion with reporting, like
> > the "NO SENSE" and "RECOVERED ERROR" series of errors.
> >
> > >
> > >  What is the behaviour initiators can expect under the above
> > >  condition ?
> >
> > The intent is that there be no conflict.  I believe that FCP-2
> > was a bit less bald than FC-PLDA in stating the requirement.
> >
> > >  Is there a conflict in the behaviours described by FCP/FCP-2
> > >  & FC-PLDA ?
> > >
> >
> > Bob Snively                        e-mail:    rsnively@brocade.com
> > Brocade Communications Systems     phone:  408 487 8135
> > 1745 Technology Drive
> > San Jose, CA 95110
> >
> > >  -----Original Message-----
> > >  From: Santosh Rao [mailto:santoshr@cup.hp.com]
> > >  Sent: Thursday, July 05, 2001 12:15 PM
> > >  To: T10 Reflector; Fibre Channel T11 reflector
> > >  Subject: FCP_RSP Residual Checking.
> > >
> > >
> > >  All,
> > >
> > >  I've got a question on target behaviour while sending a
> > >  CHECK CONDITION
> > >  SCSI status in its FCP_RSP IU.
> > >
> > >  Is the target required to initialize the fields FCP_RESID_UNDER,
> > >  FCP_RESID_OVER & FCP_RESID when any I/O is completed without the
> data
> > >  phase having transferred exactly FCP_DL bytes, regardless of the
> SCSI
> > >  Status being returned ?
> > >
> > >  When the target generates a CHECK CONDITION on an I/O and may
> have
> > >  returned less than FCP_DL bytes in the data phase for that I/O,
> is it
> > >  required to set the FCP_RESID_UNDER to 1 and indicate the number
> of
> > >  bytes not transferred in the FCP_RESID field?
> > >
> > >  FC-PLDA Section 8.2.4.1 states that :
> > >  "SCSI targets that transfer less than FCP_DL bytes during
> > >  the FCP_DATA
> > >  IUs shall set the FCP_RESID_UNDER to 1".
> > >
> > >  No exceptions are specified in the case of a CHECK CONDITION in
> the
> > >  above definition, implying that FCP_RSP residual checking can be
> > >  performed irrespective of the SCSI Status that was returned in
> the
> > >  FCP_RSP.
> > >
> > >  However, the wording descriptions of FCP_RESID_UNDER,
> > >  FCP_RESID_OVER &
> > >  FCP_RESID in SCSI-FCP & FCP-2 are not as stringent as
> > >  FC-PLDA and do not
> > >  mandate that FCP_RESID_UNDER shall be set when the data
> > >  transferred is <
> > >  FCP_DL.
> > >
> > >  What is the behaviour initiators can expect under the above
> > >  condition ?
> > >  Is there a conflict in the behaviours described by FCP/FCP-2
> > >  & FC-PLDA ?
> > >
> > >  Thanks,
> > >  Santosh Rao
> > >
> 
> --
> Education is when you read the fine print.
> Experience is what you get if you don't.

-- 
Finish each day and be done with it.  You have done what you could;
Some blunders and absurdities have crept in; Forget them as soon as you
can.
Tomorrow is a new day; You shall begin it serenely and with too high a
spirit 
to be encumbered with your old nonsense.