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RE: Portal group discovery



I guess my confusion with portal group is fully understanding the way it is
supposed to be used.
 
When a portal group is used for multiple connections in session,
the cmnSN must be monotonic and shared among all the ports-
so this indeed is a shared state, and it cannot work with multiple routers.
 
However, if all I want to achieve is multipath fail-over, I can have multiple sessions,
or MCS - but with only one session active. In both cases, the initiator can use an
alternative session or connection, and the cmdSN will advance just fine.
 
From all the answers, I understand now that portals are indeed for MCS, and failover
using multiple devices such as routers, needs to use multiple sessions (active+standby),
and that distinct devices, even providing the same service - access to same "real target",
should not, and must not be part of the same portal group.
 
Dan


From: Julian Satran [mailto:Julian_Satran@xxxxxxxxxx]
Sent: Wednesday, October 04, 2006 9:04 PM
To: Dan Bar Dov
Cc: ips@xxxxxxxx; John Hufferd; William Studenmund
Subject: RE: Portal group discovery


Dan,

The portal groups have to share more than a target name - they'll have to have some common state (the CmdSN etc.).
If behind the routers there is only the "real" FC target I don't see how you can build a portal out of several routers. If the target function is in the "real target" it might as well know who all its front-ends are.

Julo


"Dan Bar Dov" <danb@xxxxxxxxxxxx>

03/10/06 12:00

To
<ips@xxxxxxxx>
cc
"John Hufferd" <jhufferd@xxxxxxxxxxx>, Julian Satran/Haifa/IBM@IBMIL, "William Studenmund" <wrstuden@xxxxxxxxxxxxxxxxx>
Subject
RE: Portal group discovery





Let me try to explain how it can and does happen.
 
Our iSCSI target device is a "gateway" (or router). It provides FC SAN
targets to iSCSI SAN. The iSCSI target name is generated from the FC WWNN.
 
When there are more then one such routers in the iSCSI SAN, it is possible and normal
for two (or more) iSCSI routers to expose the same FC target. This is not by mistake,
rather, it allows fail-over between such routers, where the initiator uses the multiple portals
for failover.
 
Given such a configuration, how does the initiator discover it?
option 1: the routers have "cluster awareness", one router can combine information from the whole
router cluster for sendTargets response.
option 2: the initiator is configured with multiple discovery addresses - one per router.
 
If option 2 is used, then the initiator needs to combine information discovered in discrete sendTargets
responses and produce portal groups.
 
My question relates specifically to that situation - it is not clear from the iSCSI spec, if such failover
between portals (with the same pgt) discovered in discrete sendTargets responses is allowed.
 
Thanks,
Dan
 
 


From: Julian Satran [mailto:Julian_Satran@xxxxxxxxxx]
Sent:
Friday, September 29, 2006 8:05 AM
To:
William Studenmund
Cc:
Dan Bar Dov; ips@xxxxxxxx
Subject:
Re: Portal group discovery



This is not supposed to happen (getting partial data in a session)

If it happens it can be the result of a reconfiguration (between the two discovery sessions).


Julo



William Studenmund <wrstuden@xxxxxxxxxxxxxxxxx>

29/09/06 05:31


To
Dan Bar Dov <danb@xxxxxxxxxxxx>
cc
ips@xxxxxxxx
Subject
Re: Portal group discovery







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Hash: SHA1

On Sep 28, 2006, at 7:59 AM, Dan Bar Dov wrote:

> Is it allowed for an initiator to create a single portal group from  
> information
> collected from two (or more) sendTargets discovery sessions?

I don't think you need two or more SendTargets discovery sessions.  
You are supposed to hear about all portals in one SendTargets  
response, so it's supposed to all be there.

If you had very separate off-load cards, I could see that not being  
followed. But then chances are you can't have a session span said  
cards anyway. :-)

Take care,

Bill
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