Jumbo Frames worth the effort?

[jeffreywhunter]

Looking at what performance enhancements I can make to optimize my new unRaid 6.0.0 system.  Found this link (http://lime-technology.com/wiki/index.php/Improving_unRAID_Performance) and working through it.  Found the discussion on Jumbo Frames.  My mobo has the Realtek 8111F gigabit on the motherboard.  If I set the MTU=9000 as suggested on the Server, do I also have to set the MTU on each device, or is that something that the nics negotiate?

[reluctantflux]

With MTU, it needs to be the same across the board.  If any is lower than anything else, it'll always use that lowest value.  So if you're going to do it, set it on your router, your switches, your server NIC, and any HTPC client NICs.  Anything else can use the smaller packet size, but it's the machines that'll be accessing the large files the most that you want to make sure have it enabled.

[jeffreywhunter]

I'm assuming this would only apply to wired devices?  Most of my devices are wireless.  I really only am concerned about the connection between my NAS and Workstation (lots of files moved).  Rarely move files between other devices...

[reluctantflux]

Yeah, wireless is a different ball game.  As long as all items that pass the data between the NAS and Workstation have their MTU's set to 9000, you should be good to go.  Let me see what kind of performance increase you see.  I've thought about doing it in the past but just haven't gotten around to it.

[jeffreywhunter]

Cool, that's what I was hoping for.  When the connection is established between the Server and the Client, they negotiate the frame size.  Smaller frame wins.  So if I have the following

 

Server - MTU=9000

Client1 - MTU=9018 (default win7 setting for jumbo I think)

Client2 - MTU=1558 (default eth setting)

 

When client1 connects with server, the frame size is negotiated to 9000 (server limit)

When client2 connects with server, the frame size is negotiated down to 1558 (client limit)

 

Is this correct?  Will the server be able to negotiate with multiple clients at a time?  1 with jumbo frames and one with standard?

[reluctantflux]

I believe that is how it would work, yes.  But you must have a switch or router in between the devices.  If it's an unmanaged switch, you may not be able to make that change.  If you have a router, you should be able to make the change, and just make sure the two devices are plugged into that router.

 

In your example, Client2 may have a performance hit lower than if the whole string was set to 1558.    If you're going to be using different frame sizes, you'll get the best performance with VLAN tagging and separating your jumbo frame devices from non jumbo frame devices.

 

Here's a good article. I linked to the end to kind of give a bullet point view, but the whole article explains jumbo frames really well.

http://www.smallnetbuilder.com/lanwan/lanwan-features/30201-need-to-know-jumbo-frames-in-small-networks?showall=&start=4

 

I hope that helps and isn't too confusing.

[dgaschk]

Cool, that's what I was hoping for.  When the connection is established between the Server and the Client, they negotiate the frame size.  Smaller frame wins.  So if I have the following

 

Server - MTU=9000

Client1 - MTU=9018 (default win7 setting for jumbo I think)

Client2 - MTU=1558 (default eth setting)

 

When client1 connects with server, the frame size is negotiated to 9000 (server limit)

When client2 connects with server, the frame size is negotiated down to 1558 (client limit)

 

Is this correct?  Will the server be able to negotiate with multiple clients at a time?  1 with jumbo frames and one with standard?

v

This is undefined. The RFC states that all LAN hosts will use the same MTU. Use VLANs as described.

[jeffreywhunter]

@reluctantflux - thanks for the link.  Helpful.  I have a Netgear GS108E which supports vlan.  I'll give that a try and see what happens...

[korpo53]

In general, jumbo frames don't get you much apart from lowered CPU usage under heavy load. Given that your box listed is a quad core 4.2Ghz thing, CPU usage is probably not a big deal.