Re: iSCSI: ISIDs

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

David said:
"Recoverable session resources would be associated with the combination
of <iSCSI Initiator Name, TSID> at the iSCSI Target, and the initiator
tracks via <iSCSI Target Name, TSID> - in both cases the TSID replaces
the ISID."

Jim, & David, please correct me  but I think this means that only one
Session could be started from any iSCSI Initiator Node to a Given Target.
We previously permitted multiple sessions, since a number of vendors
thought Single Connections pre session was simpler to implement and did not
want to implement Multiple Connections per Session.  They were going to
continue (as they did in Fibre Channel) to rely on the "Wedge" driver
approach.

Now the Wedge Driver has not really a been defined as an SCSI construct, it
just does a job that has been needed in connections like Fibre Channel.
The ISID is what permits this case (of multiple individual connection
sessions) to operate while sharing the same authentication space (iSCSI
Node Name) with the other Sessions connected from the same Host to the same
iSCSI Target Node.

Many of us thought that Multiple Connections per Session was a better
approach, but still a number of vendors saw simplicity in Single
Connections per Session.  The implication of that is they need the ability
to bring multiple of these single sessions together via a Wedge Driver. And
hence the need for ISID.



.
.
.
John L. Hufferd
Senior Technical Staff Member (STSM)
IBM/SSG San Jose Ca
Main Office (408) 256-0403, Tie: 276-0403,  eFax: (408) 904-4688
Home Office (408) 997-6136
Internet address: hufferd@us.ibm.com


Black_David@emc.com@ece.cmu.edu on 09/06/2001 02:40:19 PM

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


To:   ips@ece.cmu.edu
cc:
Subject:  iSCSI: ISIDs



Time to back up and regroup on this topic.  It's clear that ISID
management needs more attention, and hence there are some issues
more basic than the attempted consensus call to work out.  So,
I'm going to abandon the attempted consensus call, and try to
make progress on the underlying ISID issue.  Those whose posts
have called ISID management into question should not feel it
necessary to apologize - this is an important issue to unscramble.

A rough summary of where we find ourselves is:
- iSCSI Initiator Names span network interfaces/adapters,
     as do iSCSI Target Names.
- Multiple sessions are allowed between an iSCSI Initiator
     and Target.  These are identified by an ISID and a
     TSID.
- The ISID is the Initiator portion of the Session identifier
     and is used to track certain resources associated with
     the session (e.g., persistent reserves).
- The TSID is the Target portion of the Session identifier,
     and serves primarily to make sure that all session
     identifiers (SSID = ISID||TSID) are unique at the
     Target.

Michael Schoberg suggest getting rid of the ISID:

> ISID - initiator-defined session-identifier
>
> Since initiators don't know about other initiators connected to this
target,
> this has the potential of causing problems.  Eliminate it.  The initiator
> should simply state it's intentions of establishing a new session or
adding
> a connection to an existing session (via binary flags).

The implication of this would be to make SSID = TSID, dynamically
assigned by the Target (0 is a reserved value on Login asking Target
to do this assignment), and partitioned appropriately across interfaces.
Recoverable session resources would be associated with the combination
of <iSCSI Initiator Name, TSID> at the iSCSI Target, and the initiator
tracks via <iSCSI Target Name, TSID> - in both cases the TSID replaces
the ISID.  From a functional standpoint, this looks like it works,
and has the nice additional property that session resources can be
recovered through any iSCSI Initiator interface vs. having to go back
to the one that's allowed to use the ISID for that session if ISIDs
are statically partitioned.

Does this cause any problems for the SAM-2 to iSCSI mapping?

Thanks,
--David

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