Using Putty or terminal log into your ESX/ESXi 4.x host and run the following commands. Read the descriptions before you run the commands
NOTE: I ran these commands after I install and setup the iSCSI switch in order verify MTU 9000 (Jumbo Frames)
To list all the kernels and information
Change the MTU of the kernel
Check to make sure everything work as you wanted.
esxcfg-vmknic -m 9000 KERNEL_NAME
List all of the vSwitches
Change the MTU of the vSwitch
List the switch to verify changes were made.
esxcfg-vswitch -m 9000 SWITCH_NAME
NOTE: even though everything looks correct I usually reboot the server so that it loads all o the changes on boot, you might find it helpful to recheck if problems arise later.
If you want to check the MTU on everything run the following:
This checks the whole path is working with jumbo frames (9000 will not work as a few bits are added making it over 9000)
vmkping -s 8000 <ip address of iSCSI storage>