Subject: Re: iSCSI: same ISID

From: "John Hufferd" <[email-masked]>
Date: Thu, 20 Dec 2001 11:55:54 -0800

Eddy,
The purpose here is not what you are looking at.

First, the Target iSCSI (SCSI) Port can inspect all the session arriving at
its Portal Group, to see if any have the same Initiator name and ISID as
another one.  If so, it is Not Logged-in.  This would be parallel Sessions
from the same initiator.

Second, when an Initiator comes back after a failure, they should use the
same ISID they had previously, thereby permitting approprate Nexus to be
continued e.g. Persistent Reserves, etc.

The second point was the primary reasons for the Conservative reuse.
Before this statement, some folks were using a different ISID for each
Target Node with which they were working.  Then the ISID space could get
used up, and then as sessions were stopped and restarted, they would
retrieve an ISID from an available pool of ISIDs, and as a result, the
approprate Nexus could not be re-established.  Hence the words Conservative
Reuse means you keep reusing the same ISID number as often as possible.

Therefore, you will probably see an individual Initiator have only 1 ISID,
ever used.  It is only when a Wedge Driver of some type permits Multiple
Initiators from the same Host, that you are likely to see the same
Initiator Name, and Different ISID.  But Still, into any one portal group
and Target iSCSI (SCSI) Port there will only be one active "Initiator Name
+ ISID" entity.  Each unique "Initiator Name + ISID" are treated (today) as
if they are as different as if they came from different hosts.

.
.
.
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, Cell: (408) 499-9702
Internet address: [email-masked]

"Eddy Quicksall" <[email-masked]>@ece.cmu.edu on 12/20/2001
10:39:27 AM

Sent by:    [email-masked]

To:    "ips@ece. cmu. edu \(E-mail\)" <[email-masked]>
cc:
Subject:    iSCSI: same ISID

Section 9.1.1 says:

 the same ISID should be used in the Login process to multiple

 target portal groups (of the same iSCSI Target or different iSCSI

 Targets).  Note that the ISID RULE (2.5.3) only prohibits reuse to

 the same target portal group.  It also does not "preclude" reuse to

 other target portal groups.

 The principle of conservative reuse "encourages" reuse to other

 target portal groups.  When a SCSI target device sees the same

 (InitiatorName, ISID) pair in different sessions to different target

 portal groups, it can identify the underlying SCSI Initiator Port on

 each session as the same SCSI port (in effect, it can recognize

 multiple paths from the same source).

This is good but the target will still have to sort out ISID's when they

are different under the same situations named above. So, since the

target still has to have all the code to sort this out, what good is

this statement?

I think the only thing keeping us from saying you MUST use the same

ISID's is the fact that we have allowed an iSCSI Initiator to have more
than

one session to the iSCSI Target Portal Group. Is that really necessary? If
not,

then we could make this a MUST and simplify the target code.

Eddy