Jumbo frames help

[techwise]

I have a Netgear managed switch that has 4 gige ports. 3 servers use those ports all with gige cards. All cards and the switch support frames up to 9216.

However, when I set the switch and cards in the servers to use anything higher than 1500MTU I can not get any better throughput. In fact when set to 9000 i get like 40kb. At 1500 ill get 140Mb.

The only non spec hardware is the cat5e instead of cat 6 but I know I should be getting better than 140Mb on cat5e.

I tried mant different MTU settings between 1500 and 9216.

Any ideas.

Thanks

Mike

[E1PHOTON]

A larger MTU won't really speed up your throughput significantly. A larger MTU will just decrease the number of interrupts your processor/NIC has to deal with.

The smaller throughput is probably caused by one of two factors: MTU mismatch or interfaces can't handle large MTUs. I would use tracepath to see where the MTU falls off.

James

[techwise]

James, thanks.

I do know that the hardware (in this case 3 NICs and one switch) all support jumbo frames. The switch is the limiting unit only capable of 9216MTU.

Excuse my networking ignorance. When networking between Gb capable hardware my speed between the Gb devices is less than half what it should be (I think). I assumed that would be related to the small default frame size. But from what you said, its not or only slightly. That I understand. But, what else could be the issue? These devices are all physically in the same rack with quality cables and all the hardware is set to run at Gb speed.

Im only getting like 140+-Mb and should be getting at least 350.

I know that when having the MTU on all devices set high (like 9000) the switch seemed to choke. I would watch on the receiveing server and never see the sending server make a connection. So thats a clue. Perhaps the switch just isnt up to the task. But thats surprising because it seems like a decent unit.

Cheers

[E1PHOTON]

Let's clear up some confusion I'm having now ;-)

Now that switch is 10/100 with 4 gigabit ports. All of your gigabit NICs are in the gigabit interfaces, right?

Now when you say 140Mb/s do you mean Megabyte or Megabit?

And, are you doing this from Memory-to-Memory (ie: iperf) or are you going Disk-to-Disk?

There are a plethora of factors that could cause this, but we'll start here ;-)

[techwise]

Let's clear up some confusion I'm having now ;-)

Now that switch is 10/100 with 4 gigabit ports. All of your gigabit NICs are in the gigabit interfaces, right?

Now when you say 140Mb/s do you mean Megabyte or Megabit?

And, are you doing this from Memory-to-Memory (ie: iperf) or are you going Disk-to-Disk?

1. Yes, all 3 servers are in the Gb ports and all ports are set for ethernet and all ports have Max MTU set to 9216.

2. Megabit

3. When transferring from serverA to serverB, Ill run "iftop" on serverB to monitor the traffic on the card.

Thanks.