Re: iSCSI draft 02: digests

[Mark Bakke <mbakke@cisco.com>]

Yes, the connection should not be recovered, but the iSCSI session
can be.

--
Mark

julian_satran@il.ibm.com wrote:
> 
> Mark,
> 
> I also gave it some more thought.
> 
> Since a digest failure is a transport failure that went undetected by TCP
> dropping and restarting a connection won't do us to much good - if we use
> the same link we may end up having some more.
> 
> We should treat them as iSCSI failures and have iSCSI restart the command
> without restarting the connection.
> 
> Regards,
> Julo
> 
> Mark Bakke <mbakke@cisco.com> on 05/12/2000 00:18:28
> 
> Please respond to Mark Bakke <mbakke@cisco.com>
> 
> To:   Julian Satran/Haifa/IBM@IBMIL
> cc:   ips@ece.cmu.edu
> Subject:  Re: iSCSI draft 02: digests
> 
> Julian-
> 
> Here's what we had in mind for recovering from digest/CRC failures:
> 
> 1. If the digest failure is on a command, status, or iSCSI header,
>    this means that a length field could be corrupted.  This should
>    not happen often, but it may be possible to re-send the command
>    if both the initiator and target can do session recovery as in
>    the iSCSI spec.  In any case, the connection should be terminated,
>    and a new one built in its place.  If session recovery is supported
>    and is successful, the missing iSCSI PDU(s) during and after the
>    digest failure are re-send, re-responded, and no harm done.  If
>    session recovery fails, the upper SCSI layer must receive the
>    failure, and do whatever recovery is necessary.  In any case, the
>    old connection should not be used after the failure.
> 
> 2. If the digest failure is on a SCSI data block, iSCSI length fields
>    are not affected, so there may be a possible way to resend the
>    data.  However, doing this is probably not worthwhile, so I think
>    that in the data digest case, the same recovery as in (1) should
>    be used.
> 
> --
> Mark
> 
> julian_satran@il.ibm.com wrote:
> >
> > Like on a data failure on any bus. Raise a check condition and end the
> > command with an error but let it go up to
> > the normal end.  I will spec it.
> >
> > Thanks,
> > Julo
> >
> > Matt Wakeley <matt_wakeley@agilent.com> on 29/11/2000 01:39:22
> >
> > Please respond to Matt Wakeley <matt_wakeley@agilent.com>
> >
> > To:   ips@ece.cmu.edu
> > cc:
> > Subject:  iSCSI draft 02: digests
> >
> > In appendix A is a (brief) description of the iSCSI header and data
> > digests.
> >
> > What is the expected behavior if there is a digest failure?  Just throw
> the
> > PDU away?
> >
> > -Matt
> 
> --
> Mark A. Bakke
> Cisco Systems
> mbakke@cisco.com
> 763.398.1054

-- 
Mark A. Bakke
Cisco Systems
mbakke@cisco.com
763.398.1054