RE: MC/S vs multiple sessions

I'm not aware of any need to ensure no I/O to the same LUN travels down
another session (I-T-L nexus) while I/O is pending for the LUN on the
first session (I-T nexus).

Not sure which drivers are being referred to here when you say "most wedge
drivers do not send I/O for the same LUN down different sessions (I-T
nexi)."

Most MPIO drivers I am aware of will all send I/Os down different
I-T-L nexi of a lun to perform dynamic load balancing.

Perhaps you were referring to I/Os to the same LBA range of a LUN.
Serializing I/Os to the same LBA ranges of a LUN is the job of the upper
layer application that owns the content residing on the lun such as a
filesystem, database, etc.

To answer Yanling's question, I think both solutions are equally feasible
and the debate over MPIO vs. MC/S has been a long one in the past with
marginal benefits from MC/S compared to utilizing existing MPIO
infrastructure, avoiding command ordering bottlenecks, avoiding the
creation of multiple layers performing very similar functionality.

Thanks,
Santosh


On Wed, 1 Nov 2006, John Hufferd wrote:

> 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]
>
>
>
>


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