To enable jumbo frames.
Since Jumbo Frames are not enabled by default. It can't since when you install ESXi 4, by default there is only one vSwitch and console and then you only start to build your network configuration. And you will not want to enable jumbo frames for ALL your networks and switches neither.
So to enable Jumbo frames yo must go to “unsupported mode” first (vmware KB) and enter some CLI (command line interface) commands . Or you can use VMware vMA (Vmware management assistant) – a virtual appliance to connect to ESXi and do it in CLI.
Before you start verify that your switches are compatible 802.1AD.
You must enable jumbo frames on every hop in the network otherwise it won't work and you'll find yourself in a possition that the performance on the storage network will actualy be worse than with Jumbo frames disabled.
- Login over SSH to your ESXi
$ esxcfg-vswitch -l… that will list the current MTU
$ esxcfg-vswitch -m 9000 vSwitch0… set the MTU to 9000 (Jumbo Frames)
$ esxcfg-vswitch -l… verify the change
- … repeat for your other vSwitchs …
$ esxcfg-nics -l… verify that every NIC has the new MTU-Value
Reboot to see that the changes are persistent.