after weeks of reading about jumbo frames, I change the value of mtu on my switches to 9000 catalyst 3750.
I have 2 location MAN connected by fiber channel. 4 swith cat3750 10/100/1000 on each site. Many of our server have giga nic, connected to this switch with 1000. I'm wondering if there are some issue with server 100Mbit link connected to this switch port with mtu set to 9000 and if the router also with ethernet connection with mtu to 1500 have problem with office WAN connected.
If you enable all equipment can support and enabled fragmentation then it may works. If you client / user only accept 1500 but one of the component in the network not support fragmentation then it cannot deliver to the client. You also need to match the MTU at both ends in a connection.
I'd be very reluctant to experiment with this unless I had a clear objective in mind - for example to speed up a terabyte-sized network backup. It will only make a difference if your servers are putting jumbo frames on the wire in the first place (and if the device at the other end of the connection is configured to pull the jumbos off the wire too).
Without such an objective you might find that you gain nothing except extra complexity.
I'd test as follows:
1) time a large file transfer (or whatever transaction you're looking to speed up)
2) implement jumbo frames on the nics,switches,etc
3) time the transfer again to check for an improvement