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MTU 8100 on Gigabit SAN

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Jacob Altman
MTU 8100 on Gigabit SAN
on Jan 22, 2010 at 3:45:36 am

Hi Bob,

You mention in several places to use an MTU of 8100 to avoid packet fragmentation, makes complete sense. Our switch does not offer any customzable settings for Jumbo Frames other than on/off for all ports. If I set up MTU 8100 at either end, will the switch simple pass the packets through at 8100?

Many thanks in advance...


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Bob Zelin
Re: MTU 8100 on Gigabit SAN
on Jan 22, 2010 at 4:38:25 am

and what switch do you own ?

Bob Zelin




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Jacob Altman
Re: MTU 8100 on Gigabit SAN
on Jan 22, 2010 at 5:49:41 am

Hiya,

In this installation I have an SMC8024L2. As you know, SMC and Edge-Core are the same company and this switch offers all the required protocols at a very reasonable cost. I wouldn't buy it again though as it only offers 0.4MB Packet Buffer Memory Per Port instead of 0.75MB, which the Small Tree guys say is important for video editing...

Anyhow, back to this Jumbo Frames question. Does the switch simply pass on the packets UP TO 9k, so that if both end were set to send and receive 8100, the switch would simply pass them on?

Thanks!


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Matt Geier
Re: MTU 8100 on Gigabit SAN
on Jan 22, 2010 at 4:32:59 pm

Jacob,

If you have 8100 enabled, you can pass up to 8100 in size. If you've got 9000 enabled, you can pass 9000.

Keep in mind the motherboard is likely the same (or very similar..) - There's also a reason your Edge-corE switch is only set to 8100 as opposed to 9000 byte frames.


Secondly, you'll only pass a Jumbo Frame packet in the case of a Jumbo Frame. If you pass a Standard Frame packet on a Jumbo Frame network it flows okay...because it's less then your jumbo frame setting....

Just because you've got Jumbo Frames enabled, doesn't mean it's passing jumbo packets...just that it can which will be very integral in your video environment.

:)

Matt G
Small Tree


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Eric Hansen
Re: MTU 8100 on Gigabit SAN
on Jan 30, 2010 at 9:40:08 pm

hey matt

you definitely know more than me on this, but i just want to clarify what you wrote. the switch just has jumbo frames enabled or not. you don't set the size on the switch. i think they support packets over 9000. i also believe that all switches you guys ship have Jumbo enabled by default, which wasnt always the case. since having it on causes no harm to standard 1500 byte packets.

jacob,

the important setting is at the computer and server. 8100 is a magical number for packet efficiency. Steve at Small Tree can go into this further. but you need to have the computer and server use the same setting, otherwise you could get dropped packets. every computer you have hooked into this switch (or at least in this VLAN) must have Jumbo frames turned on and set to 8100.

e

Eric Hansen - The Audio Visual Plumber - http://www.avplumber.com


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Jacob Altman
Re: MTU 8100 on Gigabit SAN
on Feb 1, 2010 at 4:25:40 am

Hi Eric,

Thanks a lot for clarifying...

8100 it is!

I really do think a 'Best Practices' sticky could be of great value to newcomers (and myself) with all these sorts of tips in one place...



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