Fibre Channel SAN Extension over IP IP Transport Architectures
Frame Size
• Most switches and HBAs allow you to specify the maximum FC payload size (aka rcv buffer size):
– 2048 bytes for FCP, up to 2112 byes w/ ext. header – Typically does not need to be changed
• FCIP and iFCP:
– Standard maximum IP MTU = 1500 – 9180 Bytes (inc. IP Header)
• Depends on transmission media
– Some IP devices do not support jumbo frames
– If jumbo frames are not supported end-to-end, you may get better performance by reducing the maximum frame size on the FC nodes—less fragmentation
With native Fibre Channel, where distance is a factor, it's better for a FC frame to be maximum size (2KB) and consume only one credit instead of two 1KB FC frames consuming two.
When running FC over an IP network however, the Frame size should be limited to 1024 so as to avoid fragmentation. Alternatively, use Jumbo Frames if possible and available end to end.