One of the changes in the VNX platform from the previous generation EMC storage arrays is that the Failover Mode 4 is supposed to be the new default. And I say "supposed to be" because during the beta program, I did not find that this was the case. The ESXi hosts we connected in to the array all used the previously default Failover Mode of 1 (Active/Passive mode). But now I think I know why. There has been a little bit of forums/message board discussions on this and the popular thought is that "everything defaults to Failover Mode 4 now"-- but I've found that is not true-- kind of.

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Today I was able to test this out on a GA array running GA code against two ESXi 4.1 hosts. What I found is that the "default" Failover Mode 4 only applies when you're registering new hosts/initiators, but vSphere hosts register themselves to EMC arrays-- and they DO NOT register themselves with Failover Mode 4. So just because it's the "default Failover Mode" don't forget to check and set this appropriately-- and it does require a host reboot once changed.

Not sure what change needs to be made to the agent/mechanism used for this registration process, but it sounds easy enough and hopefully we'll see that change in a coming update or release. Anyways-- to "resolve" I followed the normal procedure for making the change to Failover Mode 4. From within Unisphere, I went to the Hosts tab, and on the right selected "Connectivity Status". I edited the ESXi host listed and set it to Failover Mode 4, hit OK, went back to vCenter and rebooted the host (making sure all the VMs were off and it was in maintenance mode of course).

I also logged in to each host via SSH and set the Path Selection Policy for the "VMW_SATP_ALUA_CX" SATP to Round Robin (which is VMW_PSP_RR). After the reboot I checked the Properties of a VMFS datastore on the VNX, and verified that it showed up with the ALUA_CX SATP and the RR PSP as shown:
<p style="text-align: center"><a href="http://blogs.eGroup-us.com/wp-content/uploads/2011/04/ALUA-ENABLED.jpg"></a><a href="http://blogs.eGroup-us.com/wp-content/uploads/2011/04/ALUA-ENABLED1.jpg"><img class="aligncenter size-full wp-image-4015" src="http://blogs.eGroup-us.com/wp-content/uploads/2011/04/ALUA-ENABLED1.jpg" alt="" width="729" height="237" /></a></p>