Hi!
By default, ESX accesses LUNs via the first path discovered.  In half of the cases, this will be through the partner head, which is non-optimal.  The ESX Host Utilities have a script called config_mpath, which is mainly a wrapper for esxcfg-mpath, that sets paths correctly.  I recommend you download, read the docs, and install the EHU on each of your ESX hosts.
http://now.netapp.com/NOW/download/software/sanhost_esx/ESX/
 
Share and enjoy!
 
Peter


From: Linux Admin [mailto:sysadmin.linux@gmail.com]
Sent: Wednesday, March 04, 2009 11:38 AM
To: NetApp Toasters List
Subject: FCP Partner Path Misconfigured - Host I/O access through a non-primary and non-optimal path was detected.

Hello Toasters.

I am receiving the following message from auto support: FCP Partner Path Misconfigured - Host I/O access through a non-primary and non-optimal path was detected.

I have a single cluster acting in single fabric mode and it is wired up in the following way.
Each host has an i-group on each node of the cluster for. Each of the netapp node is connected to sw1 and sw2 and hosts also has a path to sw1 and sw2.
Why would the host access luns on N2 via partner node N1



 ---------------             ---------------
{    n1    }            {    n2    }

 
    |    \                  /    |
    |     \                /     |
    |      \              /      |
    |       \            /        |


 ---------------             ---------------
{    s1    }            {    s2    }

           \              /

            \            /

             ---------------
            {    host    }