RE: iSCSI: session login and ISID

[Santosh Rao <santoshr@cup.hp.com>]

> To: ips@ece.cmu.edu, <someshg@yahoo.com> 
> Subject: RE: iSCSI: session login and ISID 
> From: "Jim Hafner" <hafner@almaden.ibm.com> 
> Date: Wed, 11 Apr 2001 13:27:28 -0700 
                            
> 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. 

Jim,

Is it not the case that the Service Delivery Port (a.k.a. SDP) comprises
of a (WWUI + session id). If this is correct, then, multiple sessions
for a given pair of WWUIs is not an attempt to establish 2 I-T nexus b/n
the same 2 names or addressed SCSI ports.

It would be 2 I-T nexus b/n 2 initiator SDPs and 2 target SDPs.

As indicated in my earlier mail on this subject, multiple sessions b/n a
given pair of WWUIs is required to deal with the following type of
configurations :

- host with 2 iSCSI initiator SDPs, init1 & init2.
- target with 2 iSCSI SDPs, tgt1 & tgt2.
- single connection sessions established as follows :
 init1 - tgt1
 init2 - tgt2

All the LUs of a target are seen through 2 different paths and these are
exported to upper layer wedge drivers that handle path failover and load
balancing. 

Failure to allow the above configuration would imply that iSCSI is
breaking wedge driver functionality as also requiring the deployment of
multi-connection session in order to achieve path failover and load
balancing features.

Regards,
Santosh


> 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.)
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