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Jumbo Frames Support [message #34271] Fri, 19 December 2008 07:53 Go to next message
digidax is currently offline  digidax
Messages: 30
Registered: March 2008
Member
From: *celebraterecords.com
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
Re: Jumbo Frames Support [message #34336 is a reply to message #34271] Wed, 24 December 2008 07:31 Go to previous messageGo to next message
piavlo is currently offline  piavlo
Messages: 159
Registered: January 2007
Senior Member
From: 132.72.41*
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?
Re: Jumbo Frames Support [message #34374 is a reply to message #34271] Thu, 25 December 2008 21:11 Go to previous messageGo to next message
digidax is currently offline  digidax
Messages: 30
Registered: March 2008
Member
From: *celebraterecords.com
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
Re: Jumbo Frames Support [message #34448 is a reply to message #34374] Sat, 03 January 2009 22:29 Go to previous messageGo to next message
23max is currently offline  23max
Messages: 4
Registered: December 2008
Junior Member
From: *bhld.de
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
Re: Jumbo Frames Support [message #34449 is a reply to message #34271] Sun, 04 January 2009 11:18 Go to previous message
digidax is currently offline  digidax
Messages: 30
Registered: March 2008
Member
From: *celebraterecords.com
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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