To improve the I/O performance for ESX Virtual Infrastructure, VMware had come out with the round robin option for both ESX and VM guests. Although is an experimental option in the ESX setting today, but I will encourage you all to try this option which provide fail over and load balancing on the storage path to connect to you SAN storage. For VM guests, you will allow allow to use this when you have RDM – Raw Device Mapping option to direct read write to the physical LUN from your SAN storage without using VMFS.

To enable this on ESX host, you need to browse to the configuration tab of the ESX host, and right click the data store and select properties, and click on manage paths option in the GUI wizard. Click on Change button after that, and choose the Round Robin (Experimental) option and click OK. You will need to go through this process 1 by 1 to ensure you had round robin from each ESX host to each of the VMFS Data store.

For VM Guests, Just right click the VM and choose edit setting, and select to the hard disk which has shown as Mapped Raw LUN on the summary tab. Click on the Manage Paths and follow by the change button, and same you can easily configure to have the Round Robin enable.

ESX Host Configuuration

Wizard View for each Data Store connection from ESX

Round Robin

Policy Option which allow to change for Round Robin

Select the option of Round Robin

VM Guests Configuration

Click on Manage Paths to continue with the Round Robin Option in the next screen

You will actually see the same display and option at the last 2 steps compare the VM guests and ESX Host