If you want to enable jumbo frames on an iSCSI port group in ESXi 4.1, you’ll need to make configuration changes at the vSwitch and VMkernel NIC level. Through trial and error, I found that I had to create the iSCSI port group from the command line instead of just enabling jumbo frames on an already existing port group. At first, I already had an iSCSI port group created. I did this via the vSphere Client. But then enabling jumbo frames from the CLI didn’t work. I had to delete the iSCSI port group first, then recreate from the CLI. Note that these commands are case sensitive, including the names of vSwitches, port groups, and VMkernel NICs. These command were completed via an SSH session directly to an ESXi 4.1 host.