Re: Multi-Path MPIO and EMC
- From: "Murphy, Sean" <Sean.Murphy@xxxxxxxxxxx>
- Date: Thu, 14 Feb 2008 08:02:44 -0600
Thanks for the info. I understand more of how this all fits together.
It seems that on the VIO-Client, the algorithm should be set to Fail_Over.
This means that only one path is used at a time (the other being fail-over).
If BOTH paths are set to the same Priority (the default is set both to
priority =1) then the default one will be the 1st path that was configured,
generally path0 or vscsi0.
Load balancing can be achieved by setting the priority of each LUN to use
one or the other path.
We are using HP Enterprise Virtual Array storage systems.
and this is what it says about setting priority:
Starting with MPIO 1.0.1.0, the path attribute "priority" has been
introduced to specify a priority for
each path to specific LUN. MPIO will select failover or fail back, according
to the settings of this path
attribute. A priority of 1 specifies a primary path and a value of 2
specifies a secondary path. Several
paths can have the same priority. If several paths do have the same
priority, MPIO will select the path
which was configured first. If primary paths are available, MPIO will always
utilize one of these paths
first. If no primary path is available, a secondary path will be used
instead. Because the MPIO algorith
"fail_over" is being used, there is only one path active per LUN at a time.
By defining a different primary
path for each LUN, a static LUN-based load balancing will be achieved
distributing the I/O load of all
LUNs across the set of I/O paths. Combined with host based striping
(partition-based striping of AIX) the
total I/O load is distributed evenly across all I/O paths and the load
balancing becomes very effective. If
all paths have the priority 1, it indicates that no load balancing is being
used.
_____
From: IBM AIX Discussion List [mailto:aix-l@xxxxxxxxxxxxx] On Behalf Of
Copper, Steve
Sent: 14 February 2008 09:08
To: aix-l@xxxxxxxxxxxxx
Subject: 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
<mailto: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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