Re: Data in SCSI Response or SCSI Data

[julian_satran@il.ibm.com]

If we colud gain something by removing the residuals I would agree. But if
we stay
within the length and having residuals is generaly not considered an error
then why
do it?

Julo

"Matt Wakeley" <matt_wakeley@agilent.com> on 08/09/2000 23:01:37

Please respond to Matt Wakeley <matt_wakeley@agilent.com>

To:   ips@ece.cmu.edu
cc:    (bcc: Julian Satran/Haifa/IBM)
Subject:  Re: Data in SCSI Response or SCSI Data




Douglas Otis wrote:

> Bob,
>
> Thanks, that helps an understanding of this PDU 0x45.  If iSCSI is to
copy
> FCP

I think this needs clarification. iSCSI is *NOT* copying FCP. iSCSI is
attempting to transport SCSI over TCP/IP.  It just so happens that the end
result looks similar to what FCP did.

> then it should send a response structure as FCP and not one or two and
> use it according to FCP.  Undefined information of what some consider
SCSI
> values cause variants in use.  I have not seen tape drives use Good Sense
> residual but vary in how Check Sense residual is presented.  If iSCSI is
to
> copy FC, then why deviate on response symmetry?  At least this provides
an
> easier bridge.  Iterative read operations will carry unused values to be
> examined and opens the door for further variants.  Status presented prior
to
> data must then ensure sequence without end confirmation.

Who said anything that status was presented before data?
iSCSI allows the LAST iSCSI PDU that completes a SCSI command to also
contain
the GOOD SCSI status in the header, so that extra overhead to send the
status
PDU.

Julian, if it will make this issue go away, maybe the residual fields
should be
removed from the data PDU.  If there is residual, it will be sent in a
status
PDU.

-Matt

>
>
> Doug
>
> > -----Original Message-----
> > From: Robert Snively [mailto:rsnively@Brocade.COM]
> > Sent: Friday, September 08, 2000 9:20 AM
> > To: 'Douglas Otis'; Stephen Bailey; ips@ece.cmu.edu
> > Subject: RE: Data in SCSI Response or SCSI Data
> >
> >
> > In FCP, because FC is a multi-protocol environment that may have
> > drivers independent of the SCSI drivers, an actual buffer allocation
> > was transmitted independently of the SCSI command.  Both overrun
> > and underrun indicators and a residual are returned.  They are
> > protocol related, not SCSI related.
> >
> > There are cases where incorrect length indications are provided
> > in the SCSI model for both under-run and over-run cases, but they
> > are rare and typically associated with legacy tape drive programs.
> >
> > Bob
> >
> > >  -----Original Message-----
> > >  From: Douglas Otis [mailto:dotis@sanlight.net]
> > >  Sent: Wednesday, September 06, 2000 6:26 PM
> > >  To: Stephen Bailey; ips@ece.cmu.edu
> > >  Subject: RE: Data in SCSI Response or SCSI Data
> > >
> > >
> > >  Steph,
> > >
> > >  Although a logical use of a residual, I can not see where it
> > >  is defined
> > >  should the allocation length be greater than the returned
> > >  length.  Should
> > >  the allocation be less than the response, this is a Check
> > >  Condition and the
> > >  residual is defined.  It would seem a residual in a case
> > >  with adequate
> > >  allocation is not interesting or defined.  Do you know where
> > >  this mechanism
> > >  you describe is defined?  In normal use, without a Check
> > >  Condition such
> > >  information is not returned to the application.
> > >
> > >  Doug
> > >
> > >  > -----Original Message-----
> > >  > From: owner-ips@ece.cmu.edu
> > >  [mailto:owner-ips@ece.cmu.edu]On Behalf Of
> > >  > Stephen Bailey
> > >  > Sent: Wednesday, September 06, 2000 3:45 PM
> > >  > To: ips@ece.cmu.edu
> > >  > Subject: Re: Data in SCSI Response or SCSI Data
> > >  >
> > >  >
> > >  > > When do you get GOOD status and residual counts on a read?
> > >  > What is causing
> > >  > > the target to get the length wrong?
> > >  >
> > >  > One example is an INQUIRY command.  The inquiry data length is
> > >  > target-specific.  Typically the CDB allocation length (and
> > >  DL) are set
> > >  > to some arbitrary large value (0xff), and the target sends back
> > >  > everything it has.  The transfer ends with success status.
> > >  >
> > >  > There can certainly be transfer residual and no SCSI error status.
> > >  >
> > >  > Steph
> > >  >
> > >
> > >
> >