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RE: iSCSI: plugfest4 issues
Julian,
Text is ok,
but please add a sentence to avoid the confusion over
Status that
occurred at the plugfest - SCSI permits
a residual
count to be returned for status values other than GOOD.
Thanks,
--David
David,
We are in violent agreement. SPC3 is
explicit about counts only when talking about extended copy. The only thing I find objectionable is to tell the
initiator when to CHECK (that is a device class/device/driver issue).
Some devices for some commands will generate
CHECK CONDITION BECAUSE they have a residual count.
That is why I would suggest the following text:
The Residual Count field MUST be valid
in the case where either the U bit or the O bit is set. If neither bit is set,
the Residual Count field is reserved. Targets may set residual count and
initiators may use it when the response code is completed at target. If the O
bit is set, the Residual Count indicates the number of bytes that were not
transferred because the initiator's Expected Data Transfer Length was not
sufficient. If the U bit is set, the Residual Count indicates the number of
bytes that were not transferred out of the number of bytes expected to be
transferred.
Julo
| Black_David@emc.com
08/03/2002 01:50 AM
| To:
Julian Satran/Haifa/IBM@IBMIL cc:
ips@ece.cmu.edu Subject:
RE: iSCSI: plugfest4 issues
|
Julian, Matching FCP's
wording resulted in a "go ask the expert" algorithm for figuring out what is required - we ought to do
better, and this is an iSCSI
protocol issue. What I'm looking for in 9.4 is: - Bits 3-6 (o, u, O, U) MAY be set by the Target and SHOULD be
checked by the
Initiator when the Response is "Command Completed at Target" no matter what the value of the Status
field is. - SCSI permits Residual
Counts to be returned for Status values other than GOOD; see [SPC2].
I believe that both of these are implied by the
current text, but since this caused
confusion at the plugfest, we ought to spell it out. Thanks, --David
--------------------------------------------------- David L. Black,
Senior Technologist EMC Corporation, 42 South St., Hopkinton, MA
01748 +1 (508) 249-6449 FAX:
+1 (508) 497-8018 black_david@emc.com Mobile: +1 (978)
394-7754 ---------------------------------------------------
-----Original Message----- From: Julian
Satran [mailto:Julian_Satran@il.ibm.com] Sent: Friday, August 02,
2002 1:43 AM To: Black_David@emc.com Cc:
ips@ece.cmu.edu Subject: RE: iSCSI: plugfest4
issues
David,
We
DO EXACTLY what FCP did - say nothing. I went
through the document - thetre is no relation mentioned and that is what we do
too.
In any case we cannot enforce a SCSI
behavior. The expectation is obvious that if SCSI hands obver
counts those will be carried by iSCSI.
I also suspect that the
trouble may be deeper than we think and I find it much more prudent to say
nothing (again as FCP did).
Julo
| Black_David@emc.com
08/01/2002 05:56 PM
|
To:
Julian Satran/Haifa/IBM@IBMIL cc:
ips@ece.cmu.edu
Subject: RE: iSCSI: plugfest4
issues
|
Julian, I think we need to do something here, as there are
clearly situations in which the residual count is
important for commands that
complete with other than good
status, making the "other point of
view" reported by Robert Russell
incorrect. Waiting for SPC-3 to do something to clarify
this isn't going to do much for iSCSI interoperability in the
short term. Since Bob Snively was the Technical Editor of FCP-2,
he tends to be correct about what FCP-2 requires or intends - I
suggest we follow FCP-2, and say that the O/o/U/u bits are valid in
all cases (of course, if none of them are set, the Residual Count
field is not valid).
Thanks, --David
--------------------------------------------------- David L. Black,
Senior Technologist EMC Corporation, 42 South St., Hopkinton, MA
01748 +1 (508) 249-6449 FAX:
+1 (508) 497-8018 black_david@emc.com Mobile: +1 (978)
394-7754 ---------------------------------------------------
-----Original Message----- From: Julian
Satran [mailto:Julian_Satran@il.ibm.com] Sent: Thursday, August 01,
2002 3:26 AM To: Santosh Rao Cc: IPS Reflector;
rdr@io.iol.unh.edu; Robert Snively; santoshr@hpcuhe.cup.hp.com; T10
Reflector Subject: Re: iSCSI: plugfest4 issues
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> Sent by:
santoshr@hpcuhe.cup.hp.com
08/01/2002 03:44 AM
|
To:
IPS Reflector <ips@ece.cmu.edu>, Julian
Satran/Haifa/IBM@IBMIL, rdr@io.iol.unh.edu 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.
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