Subject: RE: [Ips] Max iSCSI Sessions supported

From: "Ramesh Mangamuri" <[email-masked]>
Date: Thu, 29 Jan 2004 18:13:11 -0800

Based on this I understandd that if you use two different vendor HBAs on
a single Host(initiator), their ISIDs also would be different.
For example if I use two HBAs from the same vendor on a single host,
will they have the same ISID, or different ISIDs???
 
Also I wasn't clear that whether this ISID is modifiable from an end
user perpective, or it is driven by iSCSI Drivers????
-----Original Message-----
From: John Hufferd [mailto:[email-masked]] 
Sent: Thursday, January 29, 2004 5:58 PM
To: Ramesh Mangamuri
Cc: [email-masked]; [email-masked]; [email-masked]
Subject: RE: [Ips] Max iSCSI Sessions supported

If you change the ISID, even with the same Initiator node name, it is a
different initiator.  You can make that work as if it is a single
initiator with what we call a wedge driver, or what you are calling
multipathing software.   

The ISIDs can have been given a number of ways to be specified, one of
the ways is to use the OUI, that represents the Vendor ID, and then you
may use your own technique to modify the rest of the bits in the ISID
any way you wish, which makes the Total name (including the Node Name)
unique within the world. 
.
.
John L. Hufferd
Senior Technical Staff Member (STSM)
IBM/System Group, San Jose CA
Main Office: (408) 256-0403, Tie: 276-0403, eFax: (408) 904-4688
Alt Office: (408) 997-6136, Cell: (408) 499-9702
Internet Address: [email-masked] 

"Ramesh Mangamuri" <[email-masked]> 
Sent by: [email-masked] 
01/29/2004 05:43 PM 
To
<[email-masked]> 
cc
<[email-masked]> 
Subject
RE: [Ips] Max iSCSI Sessions supported

Here are some questions again.

1) What if we have multi-pathing software installed on the Host
OS(Initiator) ? 
2) How can we generate different ISIDs from the same initiator.? Is this
one configurable value?

More later ...,
Ramesh

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] 
Sent: Thursday, January 29, 2004 5:20 PM
To: Ramesh Mangamuri
Cc: [email-masked]
Subject: Re: [Ips] Max iSCSI Sessions supported

On Thu, 29 Jan 2004, Ramesh Mangamuri wrote:

> Folks,
>
> I understand that there is possibility that there can be multiple
> connections in an iSCSI session. But, Can an iSCSI initiator have more
> than one active iSCSI session simultaneously with a given target.

Yes and no.

Strictly speaking, no. Any attempt to open a second session with the
target by a given initiator would trigger session reinstatement. This
represents the fact that there can be only one I_T nexus.

However since the identifier for an initiator is both the initiator name
and the ISID, the same initiator name can be used on different sessions
if
they have different ISIDs. This situation, though, can be dangerous and
should be avoided; the target would appear as two different SCSI devices
to the initiator's OS. Most OSs won't deal well with that situation. For
instance Microsoft Windows's auto-mounting of partitions could cause the
partitions on the disk to be mounted twice.

Take care,

Bill

_______________________________________________
Ips mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/ips

---

From: John Hufferd <[email-masked]>
Date: Thu, 29 Jan 2004 22:21:41 -0800

The ISID has bits reserved for the vendor to make each of their HBAs 
unique.  All Initiators names have a Node Name and a unique ISIDs, within 
that NODE. Further all Initiators within an Initiator Node, should have 
the same NODE Name.  The format of the ISID permits a straight forward 
implementation that ensures that each ISIDs is unique within a node.  All 
this is in the specification.  Refer to 10.12.5, and formats 00b and 01b. 
And yes the specification states that the node name must be admin 
configurable, and the ISID must also be configurable for multiple HBAs 
(see 9.1.2).  There is also important information in section 3.4.3. 
.
.
John L. Hufferd
Senior Technical Staff Member (STSM)
IBM/System Group, San Jose CA
Main Office: (408) 256-0403, Tie: 276-0403, eFax: (408) 904-4688
Alt Office: (408) 997-6136, Cell: (408) 499-9702
Internet Address: [email-masked]

01/29/2004 06:13 PM

To
John Hufferd/San Jose/IBM@IBMUS
cc
<[email-masked]>, <[email-masked]>, <[email-masked]>
Subject
RE: [Ips] Max iSCSI Sessions supported

Based on this I understandd that if you use two different vendor HBAs on a 
single Host(initiator), their ISIDs also would be different.
For example if I use two HBAs from the same vendor on a single host, will 
they have the same ISID, or different ISIDs???
 
Also I wasn’t clear that whether this ISID is modifiable from an end user 
perpective, or it is driven by iSCSI Drivers????
-----Original Message-----
From: John Hufferd [mailto:[email-masked]] 
Sent: Thursday, January 29, 2004 5:58 PM
To: Ramesh Mangamuri
Cc: [email-masked]; [email-masked]; [email-masked]
Subject: RE: [Ips] Max iSCSI Sessions supported

The ISIDs can have been given a number of ways to be specified, one of the 
ways is to use the OUI, that represents the Vendor ID, and then you may 
use your own technique to modify the rest of the bits in the ISID any way 
you wish, which makes the Total name (including the Node Name) unique 
within the world. 
.
.
John L. Hufferd
Senior Technical Staff Member (STSM)
IBM/System Group, San Jose CA
Main Office: (408) 256-0403, Tie: 276-0403, eFax: (408) 904-4688
Alt Office: (408) 997-6136, Cell: (408) 499-9702
Internet Address: [email-masked] 

To

More later ...,
Ramesh

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] 
Sent: Thursday, January 29, 2004 5:20 PM
To: Ramesh Mangamuri
Cc: [email-masked]
Subject: Re: [Ips] Max iSCSI Sessions supported

Yes and no.

Take care,

Bill

---

From: [email-masked]
Date: Fri, 30 Jan 2004 09:41:19 -0800 (PST)

> user perpective, or it is driven by iSCSI Drivers????

You've now gone beyond the iSCSI spec. How two different HBAs in a single
host work together is still an open question.

There are two possibilities. One is that all of the HBAs act
independently, and that a wedge driver unifies them for the OS. John
actually talks about this in his book, and on page 145 has a diagram. How
the host OS knows to only communicate with the wedge driver, and it in
turn to the HBAs, is a question for the host OS.

The other possibility is that there is a unified HBA API that permits the
different HBAs to share a session across them. This would involve some
sort of centralized command numbering, among other things.

Both of these options are areas of open development. I know some of it's
happening in the SNIA IPS forum.

Take care,

Bill