IPS-ALL

["John Hufferd" <hufferd@us.ibm.com>]

This is just another reminder that your subject line should begin with
iSCSI:, or FCIP:, or iFCP: depending on the topic you are discussing.

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John L. Hufferd
Senior Technical Staff Member (STSM)
IBM/SSG San Jose Ca
(408) 256-0403, Tie: 276-0403,  eFax: (408) 904-4688
Internet address: hufferd@us.ibm.com


Sandeep Joshi <sandeepj@research.bell-labs.com>@ece.cmu.edu on 04/18/2001
11:21:34 AM

Sent by:  owner-ips@ece.cmu.edu


To:   ips@ece.cmu.edu
cc:
Subject:  Re: target discovery issue




just realized that the reflector is not seeing this discussion.
the question at hand is how should target discovery notification
be sent in the iSCSI world.

Mark Bakke wrote:
>
> Actually, I think that part of it is an iSCSI issue.  That is,
> if a new target is created, that's at the SCSI level.  But if I
> add an iSCSI address on which to access that target, it now must
> be discovered first by the iSCSI layer on the host, before it
> can be presented to the SCSI layer.  In this case, we would need
> to send an iSCSI event indicating that there is a new target (or
> at least that there is some change in availability of targets);
> the host would then use SendTargets to find out the specifics.
>
> This brings up Sandeep's question #2.  If I am a target, I can
> send this message either:
>
>  a) On every iSCSI connection
>
>   OR
>
>  b) On all connections to canonical targets
>
> Method a gives us better coverage, and does not require an
> initiator to keep its canonical target connection around in
> between these little sendtargets commands.  However, if an
> initiator logs into a canonical target, finds that it has no
> targets to connect to (yet), and one is added later, the
> initiator would only find out if it had kept its canonical
> target connection, unless it is using an out-of-band discovery
> mechanism.
>
> Method a will also tend to bother connections to targets
> that are doing the "real" work (data path stuff).
>
> Method b will keep these events away from the data path, and
> will not generally have to send so many events.  However, it
> would require each initiator that wanted to be notified to keep
> its canonical connection around.
>
> There is a Method C, which is a combination of the above:
>
>  c) The device will send this async event message on ONE of the
>     connections to each initiator name (formerly WWUI) that is
>     connected to it.  If one of these connections is to the
>     canonical target, the device will use that one.
>
> Method c allows the initiator to choose whether it would rather
> keep an explicit canonical target connection around (e.g. if the
> other connections have been pushed down to hardware), or whether
> it would rather not keep the connection around, and be notified
> on one of the others.  The number of messages sent by targets
> would be identical to that in method b.
>
> --
> Mark
>
> julian_satran@il.ibm.com wrote:
> >
> > Sandeep,
> >
> > I think we are deep in T10 territory - this is a SCSI issue.
> >
> > Julo
> >
> > Sandeep Joshi <sandeepj@research.bell-labs.com> on 18/04/2001 16:21:06
> >
> > Please respond to Sandeep Joshi <sandeepj@research.bell-labs.com>
> >
> > To:   Julian Satran/Haifa/IBM@IBMIL, mbakke@cisco.com
> > cc:
> > Subject:  target discovery issue
> >
> > Julian & Mark,
> >
> > Friendly reminder... the issue mentioned below may not
> > have been resolved.
> >
> > 1) Is target discovery going to be the SCSI event or will
> >    it be wrapped up as an iSCSI event ?
> > 2) Do we have to keep a session to the canonical target
> >    always open to be able to do target discovery?
> >
> > -Sandeep
> >
> > I am not sure.  There are some SCSI items in it too (SCSI handles now
the
> > appearnce of new LUs).
> >
> > I will need a longer discussion with NDT to understand the semantics.
> >
> > Julo
> >
> > Sandeep Joshi <sandeepj@research.bell-labs.com> on 12/03/2001 22:25:27
> >
> > Julian,
> >
> > in case you skip this one..
> > your response is required on point (1) for amending iSCSI draft.
> >
> > -sandeep
> >
> > Sandeep-
> >
> > The problem you pointed out in item number 1 creates the need
> > for an additional iSCSI-level event.  Since the discovery of
> > targets happens at the iSCSI level, rather than at the SCSI
> > level, how about adding this to 2.18.1 (in iSCSI-05)?
> >
> >   4   Network entity indicates that a "target discovery" event
> >       has occurred.
> >
> > Upon receiving this message, the initiator should use SendTargets,
> > or whatever other methods of discovery it is using, to find out
> > what has changed.  Usually, this would be due to adding a new
> > target.
> >
> > We will fix items 2-4; thanks for pointing them out.
> >
> > Thanks,
> >
> > Mark
> >
> > Sandeep Joshi wrote:
> > >
> > > 1) Section 4.2 last line before Section 4.2.1
> > >     "target MUST send any iSCSI-level async on this session,
> > >      allowing the initiator to discover new targets.."
> > >
> > >    The session mentioned here is a session to the canonical target.
> > >
> > >    However, the iSCSI 05 draft does not mention any such condition
> > >    in Sec 2.18 on Async Message.   In there, a SCSI event (note: not
> > >    iSCSI) is used to notify availability of new targets.
> > >