Improve your iSCSI performance using jumbo frames

What are jumbo frames? Jumbo frames are ethernet frames with more than 1500 bytes of payload. Conventionally, jumbo frames can carry up to 9000 bytes of payload, but variations exist and some care must be taken when using the term.

Why use jumbo frames? Enabling them on your network equipment and on your NICs you will experiment a performance boost specially with iSCSI protocol that works over a standard ethernet network.

Implementation of Jumbo frames must be done with some rules:

  • Same MTU for all server present in the network
  • Network card must support a MTU over 1500
  • Switch must support a MTU over 1500
  • Switch must support a MTU over 1500 on a VLAN

How to enable jumbo frames on RHEL/CentOS? Enabling jumbo frames on linux is really simple: edit the NIC configuration and append MTU=9000.

Don’t forget to enable them also on your switch/router!

# vi /etc/sysconfig/network-script/ifcfg-<your_nic> # ex. eth0


Then restart the single interface…

ifdown eth0; ifup eth0

…or the entire network service

service network restart

After all verify that the new configuration has been correctly applied:

# ifconfig eth0

If the configuration is ok you will see a response like this:

eth0      Link encap:Ethernet  HWaddr xx:xx:xx:xx:xx:xx
inet addr:x.x.x.x  Bcast:x.x.x.x  Mask:x.x.x.x

If you’re using bonding, you need to enable jumbo frames only on bond device configuration:

# vi /etc/sysconfig/network-script/ifcfg-bond0