One thing it seems is overlooked when architecting or troubleshooting a VMware solution with your SAN environment is the use of Jumbo Frames. Most Ethernet switches have Jumbo Frame support and can handle the higher Maximum Transmit Unit (MTU) This is used for a variety of reasons, and especially comes in handy if you want to use VLAN trunking or need the larger transmit size.
When there are performance issues over the network and your storage a consideration is the actual size of the Ethernet frames. The maximum is typically 9216, so it is recommended to size the payload to the maximum allowable setting. This helps makes sure to account for any extra bytes, such as, header (18 bytes), VLAN tag (4 bytes – Tag Protocol, User Priority, Cannonical Format Indicator, and VLAN ID), and addresses. If you don’t take this into account your environment will have issues communication and you could suffer severe performance issues.
How To:
1. Using vCLI connect to your ESX/ESXi host
2. Execute the following Command:
vicfg-vswitch -m <MTU> <vSwitch>
You will want to set the max MTU possible that your virtual network adapters connected can handle
3. Verify:
v icfg-vswitch –l
To Enable Jumbo Frames on a VMkernal port
1. Using vCLI connect to your ESX/ESCi host.
2. Execute the following command:
esxcfg-vmknic –a –I <ip address> -n <netmask> -m <MTU> <port
group name>
This will create a port on the VMkernal allowing for Jumbo Frames.
3. Verify:
esxcfg-vmknic –l
Conclusion:
Hopefully this is useful and could solve the mystery performance issues. Make sure you adjust the MTU on your storage array, EMC, NETAPP, Equallogic, etc.
Thanks!
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