Support for Jumbo Frames is not enabled by default in ESXi 4.1. So to enable Jumbo frames you must login using the "Tech Support Mode" or the "Remote support Mode (SSH)".

Jumbo Frames should be enabled on every hop in the network otherwise it won’t work and you’ll find yourself in a position that the performance on the storage network will actual be worse than with Jumbo frames disabled.

Prerequisites:

• We should have a ESXi host with multiple vmnics and following environment :
• Switch and NFS storage both configured for Jumbo Frames and an MTU of 9000 bytes.
• ESXi 4.1 configured with 2 vSwitches - vSwitch0 and vSwitch1
• vSwitch0 has the default MTU (1500 bytes) and connected to the VLAN facing the users.
• vSwitch1 connected to the same VLAN as the NFS Storage.
• Full permission to the Host
• Working knowledge of making changes to networking and storage.

The Process:

• Login over SSH to your ESXi host
• $ esxcfg-vswitch -l… that will list the current MTU
• $ esxcfg-vswitch -m 9000 vSwitch1… set the MTU to 9000 (Jumbo Frames)
• $ esxcfg-vswitch -l… verify the change
• $ esxcfg-nics -l… verify that every NIC has the new MTU-Value

Thats it.

Reboot to see that the changes are persistent.