RE: iSCSI: session login and ISID

["Jim Hafner" <hafner@almaden.ibm.com>]

Folks,

As the one that started the debate (somewhat privately) on whether one or
more sessions can be allowed between the same two named guys, I think I'd
better cut in here.

I'll warn you that I'm going to be vague and skip a lot of the details.

The N&DT is debating the (critical in my opinion) mapping of the SCSI
Architecture constructs of SCSI Device, SCSI Port, SCSI Nexus and the
constructs of iSCSI (things with "unique names", sessions, etc.).   This
has consequences to reservations, scsi access controls, unit attention
conditions,etc.(all those things that are essentially nexus state).  To
complicate matters, SAM-2 is evolving as we speak.

One has to keep in mind that SCSI is NOT completely stateless with respect
to individual IOs (e.g., they are not self-authenticating).  E.g., a given
IO is allowed to proceed ONLY if the nexus on which it is sent is not
blocked by some reservation state on another nexus.

Now we come to the crux of the issue. In my opinion, there is a fundamental
assumption (not explicitly stated) in the SCSI architecture that there
never exist more than one nexus between the same two (named or addressed)
SCSI Ports.  Parallel and FCP get this for free because of protocol layer
constructs/limitations.   In my opinion, iSCSI needs to make a similar
restriction to meet this requirement.  (Why SAM-x needs it at all is rooted
in the nexus state; I could go into that, but I won't unless pressed,
preferably offline.)

The net of this is that whatever mapping of SAM-2 terms to iSCSI terms we
pick, there will need to be imposed some limitations on sessions (not clear
what yet) to meet this requirement.

The N&DT will soon be offering one approach to the mapping and the
resulting requirements.  Hopefully, it will meet everyone's requirements.

Jim Hafner


"Somesh Gupta" <someshg@yahoo.com>@ece.cmu.edu on 04-11-2001 11:57:04 AM

Please respond to <someshg@yahoo.com>

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


To:   Julian Satran/Haifa/IBM@IBMIL, <ips@ece.cmu.edu>
cc:
Subject:  RE: iSCSI: session login and ISID





> -----Original Message-----
> From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf Of
> julian_satran@il.ibm.com
> Sent: Tuesday, April 10, 2001 4:22 AM
> To: ips@ece.cmu.edu
> Subject: Re: iSCSI: session login and ISID
>
>
>
>
> WWUI can be presented during login phase (2.10.9 is correct and in-line
> with 1.2.7) Two sesions can have the same ISID but will have different
> TSID. The question of whether more than one session should be allowed
> between a pair of wuis is under debate.

Why are we debating this? Multiple sessions (one
connection per session) is a simpler, more robust and higher
performance model than multiple connections per session.

Somesh
>
> Julo
>
> sandeepj@research.bell-labs.com (Sandeep Joshi) on 09/04/2001 20:27:46
>
> Please respond to sandeepj@research.bell-labs.com (Sandeep Joshi)
>
> To:   ips@ece.cmu.edu
> cc:
> Subject:  iSCSI: session login and ISID
>
>
>
>
> There seems to be a problem in distinguishing session logins, using
> only the ISID field in the Login Command.   It is possible that
> different initiators could try to start a session using the same ISID
> value.   One of those attempts will get rejected, since the ISID is
> the sole key to find if a session already exists. (note: TSID was
> sent as zero for the leading connection of session)
>
> The initiator WWUI does not seem to be available at this time.
> a) Appendix D.10 states that InitiatorWWUI is optional and defaults
>    to iSCSI.
> b) Section 2.10.9 on Login Command states that "initiator MAY provide
>    some basic parameters".
>
> On the other hand, Section 1.2.7 states that "the initiator MUST
> present both its initiator WWUI and target WWUI to which it wishes
> to connect during the login phase".
>
> The WWUI is also needed if we are to support multiple I_T nexuses
> between the same initiator and target.
>
> So it seems like Section 1.2.7 has the right spec.   Appendix D and
> Section 2.10.9 must then be corrected.  The descriptions in Sec 4.1
> and Section 1.2.3 may also need to be changed to reflect the fact
> that initiator WWUI must be supplied at session login.
>
> -Sandeep
>
>
>

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