Re: Multi-Path MPIO and EMC

Sean,

In the Redbook "Advanced POWER Virtualization on IBM System p5"
SG24-7940-01, there is a section 5.4.3 "Working with MPIO on client
partitions". It details 2 steps that you should take when setting up the
clients, one is setting the hcheck_interval and the other is setting the
priority path.

".....Note: MPIO on the client partition runs a fail_over algorithm.
That means only one path is active at a time. If you shut down a Virtual
I/O Server that serves the inactive path, then the path mode does not
change to failed because no I/O is using this path.

Set the path priority for this partition to have the active path going
over VIO_Server2. The default setting is priority 1 on both paths, as
shown in Example 5-20. In this case, you do not need a special path and
the system will pick path0 as the active path. Priority 1 is the highest
priority, and you can define a priority from 1 to 255........"

So Keith is correct in the fact that only one path is used at a time but
as my setups are based upon this information in the redbook I am
seriously hoping that they are supported!



Regards
Steve

________________________________

From: IBM AIX Discussion List [mailto:aix-l@xxxxxxxxxxxxx] On Behalf Of
Keith Stevenson
Sent: 13 February 2008 19:07
To: aix-l@xxxxxxxxxxxxx
Subject: Re: Multi-Path MPIO and EMC


Sean,

I'm not sure that is a supported configuration for VIO based disks. I
found the following in the "System p Advanced POWER Virtualization Best
Practices" Redbook.

"The MPIO support of virtual SCSI between client partitions and dual
Virtual I/O Servers only supports failover mode. For any given virtual
SCSI disk, a client partition will use a primary path to one Virtual I/O
Server and fail over to the secondary path to use the other Virtual I/O
Server. Only one path is used at a given time even though both paths can
be enabled."

In general, given a dual VIO server environment, I tend to set things up
so that under normal circumstances virtual ethernet traffic runs through
one VIO server and the virtual SCSI traffic runs through the other.
Both are configured for failover so that either VIO server may be taken
down for maintenance without impacting the client LPARs.

Regards,
Keith Stevenson
IBM System Architect



On Feb 13, 2008 10:48 AM, Murphy, Sean <Sean.Murphy@xxxxxxxxxxx> wrote:


Thanks Steve,

the priority is the same for both paths (i.e. vscsi1 and vscsi0
are set to prioity 1)
However I noticed that the algorithm on the vio server is set
to round_robin.

I guess this means that the load is balanced to each path 50/50.



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