RE: MC/S vs multiple sessions

To the above - only a tiny caveat - your iSCSI driver (initiator and 
target) must really use both connections. Some drivers do it better than 
others and even use the connections to asure a modicum of QoS. The 
restriction that most MPIOs introduce as John mentioned is due to the need 
of many applications to keep ordering.

Julo



"John Hufferd" <[email protected]> 
01/11/06 16:25

To
"Qi, Yanling" <[email protected]>, <[email protected]>
cc

Subject
RE: [Ips] MC/S vs multiple sessions






Because of I-T-L Nexus issues, most wedge drivers (such as MPIO) do not 
send I/O for the same LUN down different Sessions.  Even if they do, they 
need to ensure that no I/O for the same LUN travels down another Session 
while I/O for that same LUN is pending on the first session.
 
With Multiple Connections per Session (MC/S), there are no such 
restrictions.  Therefore the Initiator can send commands for the same LUN 
down both connections at a rate that is only limited by the ability of the 
storage controller to handle it.  It is also true that with MPIO commands 
for other LUs can occur on the other Paths, but this may or may not be the 
process which is most acceptable to the total environment. 
 
What this means is that performance is generally better with MC/S, but the 
degree of performance improvement will depend on the design of the Wedge 
Driver (MPIO) and the quantity of Multiple I/Os to the same LUN.
 
.
.
.
John L Hufferd
Sr. Executive Director of Technology
Brocade Communications Systems, Inc
[email protected]
Office Phone: (408) 333-5244; eFAX: (408) 904-4688
Alt Office Phone: (408) 997-6136; Cell: (408) 627-9606
 

From: Qi, Yanling [mailto:[email protected]] 
Sent: Wednesday, November 01, 2006 8:43 AM
To: [email protected]
Subject: [Ips] MC/S vs multiple sessions
 
Assume my iSCSI target device has two network portals and my initiator 
device has two network portals as well.  I could create two sessions or 
create one session with two connections between the initiator and target. 
I do have MPIO service on the initiator host that provides IO load balance 
cross the two sessions. I could not see the differences from the viewpoint 
of IO availability.  Which implementation is better in term of IO 
performance?
 
Thanks,
 
Yanling
 
 
 
Yanling Qi
Engenio Storage Group - LSI Logic
512-794-3713 (Office)
512-794-3702 (Fax)
[email protected]
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