I have a group of servers on 10Gb that I want to use jumbo frames on to hopefully speed up the backups. The backup server and switches can be changed.

If I turn on jumbo frames, will all of the clients that connect to those servers with normal frames (1500MTU) cause fragments? Say the client talks the server with 1500 MTU and then will the server reply with a 9000 MTU frame causing the client to fragment it?

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    The MTU must be the same on every host within a single layer 2 network. You could setup a VLAN. – Zoredache Feb 11 '13 at 17:12
  • So you use VLAN's I would need to create a VLAN on the servers on both ends of the connection and create the VLAN/assign the VLAN to the ports on the switches right? – user1983916 Feb 11 '13 at 19:26
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    It might speed up backups, but it might not. I tested Jumbo Frames extensively when trying to tune 10GbE performance at $dayjob[-1], and found an insignificant increase in speed. YMMV – Tom O'Connor Feb 11 '13 at 23:46

I think you may be thinking of fragmentation that can happen with IP packets. With MTUs, the packet is either dropped or transmitted. There is no fragmentation. If the server transmits a packet to the client that is greater than 1500 bytes in the given configuration, it will simply be dropped and not processed, which is different to fragmentation. (Fragmentation in itself is quite a messy situation, but it's better than losing the packet as a whole.)

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