On Aug 22, 2014, at 12:07 PM, Redwood Hyd <redwood...@gmail.com> wrote:

> Hi All,
> I am trying to achieve10Gbps in my single initiator/single target env. 
> (open-iscsi and IET)
> 
> I exported 3 Ramdisks, via 3 different IP aliases to initator, did three 
> iscsi logins , 3 mounts points and then 3 fio jobs in parallel (256K block 
> size each).
> 
> Question 1) Is above a real use case where from same iscsi initiator i did 3 
> iscsi logins to same target (via different IP addresses) ? Anything pros/cons 
> with this.

This seems normal.

> 
> Question 2) What are the other best ways to create parallel TCP flows 
> (because it seems open-iscsi does'nt have MC/S support)

Multiple sessions to different portals then use dm-multipath over all those 
paths/sessions to the LU.

> Question 3) In this scenario can I use dm-multipath - can someone suggest 
> most common way so that at TCP level i get multiple flows.
> 

What you described above, when you run

/sbin/multipath
/sbin/multipath -ll

Do you see each device having 3 paths? Did you set it up to do round robin for 
dm multipath path selection? If so, each path is going to be a different tcp 
socket connection which the iscsi initiator and dm-multipath will use to send 
IO on.

At my last job, fusion-io/sandisk, we sold a high performance target, and to 
get the highest throughput when using linux we had to create extra 
sessions/connections to avoid some bottlenecks in the linux block/scsi layer.

Above you would have a session to each target portal/ip. We would set 
node.session.nr_sessions in iscsid.conf to greater than one so each portal 
would have nr_sessions sessions/connections. When you run iscsiadm -m node -T 
target -p ip -l, iscsiadm would then create nr_session to that portal. iscsiadm 
-m session would show the extra sessions when logged in and multipath -ll 
should show the extra paths.

You can also just do

iscsiadm -m session -R SID -o new

to dynamically add another session/connection.

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