Re: Multi-Path MPIO and EMC

Copper, Steve schrieb:
Sean,

Not sure how to tell exactly at a specific time which path AIX is using
but to tell which one is the preferred path (which it will use if both
paths are in the Enabled state) use the commands:-

# lspath -AHE -l hdisk38 -p vscsi0
and
# lspath -AHE -l hdisk38 -p vscsi1

If the priority number is different then the preferred path will be the
lower of the 2 values. If they are the same then I am not sure which one
it uses. It is one of the steps that I take in setting up the VIO
clients to alternate the priority path for each disk, setting one to a
value of 2 whilst the other path keeps the default of 1.

HIH

Steve

-----Original Message-----
From: IBM AIX Discussion List [mailto:aix-l@xxxxxxxxxxxxx] On Behalf Of
Murphy, Sean
Sent: 13 February 2008 14:01
To: aix-l@xxxxxxxxxxxxx
Subject: Re: Multi-Path MPIO and EMC

Is there any command that can tell you which path AIX is using to access
a LUN at any one time.

e.g. #

lspath -l hdisk38
Enabled hdisk38 vscsi0
Enabled hdisk38 vscsi1

vscsi0 is vio server A and vscsi1 is vio server B.

I would like to see which Vio server A or B is being used.

Thanks



-----Original Message-----
From: IBM AIX Discussion List
To: aix-l@xxxxxxxxxxxxx
Sent: 13/02/2008 07:25
Subject: Re: Multi-Path MPIO and EMC

Larry,

AIX MPIO first became available in AIX 5.2, so you're going to need an
upgrade just to get it. (There are lots of other reasons to move off of
5.1, but I won't belabor the point.)

Once you have MPIO, AIX will recognize that it can access a given device
over multiple fscsi devices. It will present a single hdisk to LVM for
use. The underlying paths can be seen via the lspath command.

Native MPIO uses a path failover algorithm. All access will drive down
a single path unless communications are interrupted. Only then will it
use an alternate path. More advanced algorithms (i.e. round-robin) are
provided by the storage vendor's device specific driver. (In your case,
PowerPath.)

Regards,
Keith Stevenson
IBM System Architect


On Feb 13, 2008 6:40 AM, Larry Scheetz < LScheetz@xxxxxxxxxxx
<mailto:LScheetz@xxxxxxxxxxx> > wrote:


Admins,





Does anyone have documentation on setting up MPIO for Multi Path? I
don't have experience with this and need to setup a duel path for my
disks on EMC. Environemtn is a P630 (System Model: IBM,7028-6C4)
running AIX 5.1.0.0 <http://5.1.0.0> and external disks on EMC box. I
do not have Power-Path from EMC. I do have two fiber connections to the
EMC box and can see all the disks via each path. From what I have
read, MPIO would the trick for me.



Thx

Larry



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... try:
iostat -m

.. to tell which path is used at a specific time....

Regards
Urs

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