Jumbo frames are what you need on a dedicated storage (NFS, iSCSI, DRBD) network. Since the packets are bigger, fewer packets are needed to send the same data. This results in faster transfers and less CPU overhead on both the transmitting and receiving ends. All in all, a good recipe for better performance.
Jumbo frames are enabled by raising the Maximum Transmission Unit, or MTU, the default MTU in networks is 1500. Often a value of 9000 is used to enable jumbo frames, this is an 8KB datagram, and some overhead.
The MTU can be altered using ifconfig:
ifconfig <interface> mtu 9000
To make sure this setting survives across reboots, open the file /etc/sysconfig/network-scripts/ifcfg-[interface] and add the following line:
Caveat Emptor: Make sure the MTU is the same across your network, otherwise this might negatively influence performance.