I just received an email from one one of my readers, Mike Laskowski, he wanted to share the following with us:

I have over 100+ LUN’s in my environment. Round Robin is officially supported on ESX4. In the past we had a script that would manually load balance the LUN’s across FAs. ESX4 has a different way to balance the LUN’s to round robin. What you can do is build the ESX server and then in the CLI do:

esxcli nmp satp setdefaultpsp –psp VMW_PSP_RR –satp VMW_SATP_SYMM

Note: You should do this before presenting LUN’s and adding datastore. If you already have LUN’s presented and datastore added, then you do that command and then you’ll have to reboot the ESX server to take effect. This will make Round Robin the default on all LUN’s. It would take forever if you had to manually change each LUN.

THX Mike Laskowski

Please note that this example is specifically for the “SYMM” SATP. SATP stands for Storage Array Type Plugin and Symm stands for EMC DMX Symmetrix. In case you are using a different array find out what the SATP is you are using and change it accordingly.