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Wednesday, November 14, 2012

What are Netapp Jumbo Frames and how to implement

Jumbo frame is a term applied to an Ethernet frame that carries more than the standard 1500-byte data payload. The most commonly quoted size for a jumbo frame is 9000 bytes, which is large enough for 8KB application data plus some amount of upper-layer protocol overhead.
Jumbo frames can improve performance in two ways:

1. Packet assembly/disassembly in high-throughput environments can be an intensive operation. A jumbo frame decreases the amount of packet processing operations by up to a factor of six.

2. The overhead associated with the Ethernet packet once prepared for transmission is a smaller percentage of a jumbo frame than a regular sized frame.

In testing, jumbo frames can result in a throughput increase of up to 30%.
Jumbo frames require the end points and all devices between them in the network to be configured to accept the larger packet size if they are not configured for them by default. This includes any network switching equipment. An example command to configure a Network Appliance storage system for jumbo frames is shown below:

FBTFAS01> ifconfig e9a mtusize 9000

The value for the maximum transmission unit size as configured should be added to the /etc/rc file to be made persistent. Jumbo frame support can also be configured by running the setup command again.

Larger frame sizes can be used, but the 32-bit Ethernet CRC mechanism used to generate the 4-byte Frame Check Sequence (FCS) at the end of the frame begins to lose its effectiveness at around 12,000 bytes.

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