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Jumbo Frames Support [message #34271]

Fri, 19 December 2008 07:53

digidax
Messages: 30
Registered: March 2008

Member

Hello,

where can I get informations about the possibility of my system to use jumbo frames (MTU=9000) with my NIC chipset RTL8169SC ? All other devices of the SAN (Switch, Storagecluster) are still set on MTU=9000.
I'm still using kernel 2.6.18-53.1.6.el5.028stab053.6 on a x86_64.

best regards
Frank

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Re: Jumbo Frames Support [message #34336 is a reply to message #34271]

Wed, 24 December 2008 07:31

piavlo
Messages: 159
Registered: January 2007

Senior Member

Why don't you just try

ifconfig eth? mtu 9000

on the SAN attached interface and tcpdump to see the packet sizes
it recieves.

BTW which SAN are you using?

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Re: Jumbo Frames Support [message #34374 is a reply to message #34271]

Thu, 25 December 2008 21:11

digidax
Messages: 30
Registered: March 2008

Member

Hello,

ifconfig eth2 mtu 9000 promts me an error:
SIOCSIFMTU: Invalid argument

The same NIC's are running with MTU 9000 at my SAN clusters. I'm using a selfmade SAN: the storage nodes a based on FreeNas, running in synchronous mode on different buildings as HA cluster.

A value of MTU 7000 will be accepted by the NIC on OpenVZ, so I'm thinking, the OVZ kernel / driver combination should be the problem. Thats why I'm interesting in getting informations about the NIC driver in the actual kernel.

best regards
Frank

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Re: Jumbo Frames Support [message #34448 is a reply to message #34374]

Sat, 03 January 2009 22:29

23max
Messages: 4
Registered: December 2008

Junior Member

Hi,

i think max. MTU you can use is 7200. This is as defined in
http://tomoyo.sourceforge.jp/cgi-bin/lxr/source/drivers/net/ r8169.c#L70

When you set MTU from userspace, the function rtl8169_change_mtu will be called and the supplied value is evaluated around line 2843ff and eventually set in hardware. The source is here http://tomoyo.sourceforge.jp/cgi-bin/lxr/source/drivers/net/ r8169.c#L2838

I think this explains your problem.

Regards,

Tristan-777

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Re: Jumbo Frames Support [message #34449 is a reply to message #34271]

Sun, 04 January 2009 11:18

digidax
Messages: 30
Registered: March 2008

Member

Hi,

thanks for searching the answers of my question. Yes this is it exactly what I'm looking for. I will try it in a test environment to protect the production file system if there are some frames dropped or in other misconfiguration facts

best
Frank

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