Jumbo Frames, for the uninitiated heathens out there, is basically a Ethernet frame with a payload of more than 1500 bytes, up to a typical maximum of 9000 bytes per frame. Why would I want to do this? Performance, in a nutshell. The only requirement would be that your switch supports Jumbo Frames, which I believe most, if not all, mid to high-end kit does. So let's get down to business, shall we?
I'm fairly proficient with Cisco and HP networking gear, so I'll give a quick rundown of the commands needed to enable jumbo frames on their kit:
- Cisco: Go into conf t mode and enter the following command "system mtu jumbo 9000". Once that is done issue a "reload" command to reboot your switch
- HP Procurve: On these babies Jumbo frames need to be enabled per VLAN. Execute the following command: "vlan # jumbo"
Configure Jumbo frames in vSphere
- Log on to your ESX host using your favorite SSH client
- Change your chosen vSwitch MTU with the following command "esxcfg-vswitch -m 9000 vSwitch#" Replace vSwitch# with the name of the vSwitch you want to modify
- Seeing as one cannot change an existing VMKernel port MTU, you will either have to remove and recreate your existing VMKernel port, or create a new one. To delete an existing VMKernel port, enter the following command: "esxcfg-vmknic -d -p VMKernelport"
- Now let's add a VMKernel port called "iSCSI01" to our vSwitch, like so: "esxcfg-vswitch –A iSCSI01 vSwitch#"
- Now we enable jumbo frames on our VMKernel port: "esxcfg-vmknic –a –i 192.168.x.x –n 255.255.255.0 –m 9000 iSCSI01". You do know you need to change the IP address and mask to reflect your environment, right?
- Let's make sure we didn't screw up somewhere by running "esxcfg-vmknic –l". Verify that the MTU is set to 9000
- All done! You can refer to my previous iSCSI Multipathing post to ensure Jumbo frame enabled iSCSI Multipathing goodness!