RE: iscsi : target port definition

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

What Jim said is correct, however, there will also be HBAs that know how to
coordinate their Multi Connection Sessions across Multiple HBAs.  However,
there may still be a limit to the number of such HBAs that are supported,
like that, in a single iSCSI Target Device (like a Max of 8 HBAs working
together etc.).  Or there might be other reasons not to make the whole unit
into a single Portal Group.





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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


Jim Hafner/Almaden/IBM@IBMUS@ece.cmu.edu on 09/14/2001 10:17:06 AM

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


To:   <eddy_quicksall@ivivity.com>, ips@ece.cmu.edu
cc:
Subject:  RE: iscsi : target port definition




Eddy,

That certainly fits within the scope of what I described.

However, I don't think that's the "main purpose".  As I understand it, the
whole notion of target portal group was suggested to enable HW
implementations with multiple iSCSI HBAs that (a) had multiple network
interfaces/nics (b) could coordinate sessions across the network interfaces
*within their own HBA* but (c) didn't have an additional (complex) software
layer that could coordinate sessions across HBAs.   In that case, we wanted
a simple way to describe to the initiator (in SendTargets), that even
though this target may have 4 ipaddress/tcpports available, they only work
in pairs (say) as far as multi-connection sessions (one pair of addresses
per HBA).  That information would help the initiator from generating a lot
of failed "add this connection to existing session" requests.   This model
turned out to have additional value in the SCSI modeling, so we took
advantage of it.

Jim Hafner


"Eddy Quicksall" <eddy_quicksall@ivivity.com>@ece.cmu.edu on 09/14/2001
09:50:33 am

Please respond to <eddy_quicksall@ivivity.com>

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


To:   "'Santosh Rao'" <santoshr@cup.hp.com>, "'IPS Reflector'"
      <ips@ece.cmu.edu>
cc:
Subject:  RE: iscsi : target port definition



They way I see it is the Target Portal Group is a way for target
administrators to logically group things so the initiator knows which
addresses:ports to use when establishing a nexus.

Isn't that the main purpose?

Eddy

-----Original Message-----
From: Santosh Rao [mailto:santoshr@cup.hp.com]
Sent: Thursday, September 13, 2001 8:38 PM
To: IPS Reflector
Subject: iscsi : target port definition


Hello,

I have a question on the interpretation of the iscsi target port
definition. The iscsi rev 08 defines the iscsi target port to map to an
iscsi target portal group.

Thus, any iscsi target that wishes to allow multiple SCSI paths to be
established to the target node MUST provide at least 2 iscsi target
portal groups.

The above definition of an iscsi target port somewhat alters the
semantics of a target portal group. A target portal group, by
definition, is a collection of a set of network portals within the
target across which a session can be spanned.

Thus, if a target supports a multi-connection session spanning across
all its network portals, such a target would use a single target portal
group to indicate that 1 big fat session pipe could be established to
all its network portals. This, in turn, would have the side effect of
only providing 1 scsi path to the upper layer wedge drivers, if the
iscsi initiators establish a session per target portal group. [which is
the target port].

From an initiator's perspective, what should be the target side
end-point of an initiator's sessions when it may need to support upper
layer wedge drivers ? Should the initiator establish a session per
target
portal group [, in which case the above issue exists] ? Or, should it
establish a session per TargetAddress ??

Regards,
Santosh