MTU for Dummies ?

Is there by chance a "how to set mtu for dummies" guide?
I did some searching - found some perl code - in the forums - some referenced back to 1.x etc...
Sadly searching the forums since 2.x is out has been a bit more difficult

that being said here is what I need to figure out.

We have a cluster with 8 systems in it.
We want to have that cluster use our SAN.
Our SAN is set to an MTU of 9000 on its own ip range (not vlan just ip range)

What I would like to do in each system is setup so the vmbr0 operates at its normal 1500 MTU
and each system to have the eth1 network port to use the MTU of 9000

Anyhow - I think a For Dummies write up would be excellent for those trying to figure this out.
 
Last edited:

si_faisal

New Member
Nov 13, 2011
4
0
1
Jakarta, Indonesia
do the command in console
to change mtu interface manually, test it first
ifconfig eth0 down
ifconfig eth0 mtu 9000
ifconfig eth0 up

To change it permanently, put it in the /etc/network/interfaces
Example:

iface eth0 inet static
address 192.168.0.1
network 192.168.0.0
gateway 192.168.0.254
netmask 255.255.255.0
mtu 9000
 
do the command in console
to change mtu interface manually, test it first
ifconfig eth0 down
ifconfig eth0 mtu 9000
ifconfig eth0 up

To change it permanently, put it in the /etc/network/interfaces
Example:

iface eth0 inet static
address 192.168.0.1
network 192.168.0.0
gateway 192.168.0.254
netmask 255.255.255.0
mtu 9000

Great - except it is not working .
Upon further inspection it appears the Dell 1950's eth1 card onboard has gone bad.
Dell should be here tomorrow to fix at least.

I was kind of going nuts trying to figure it out -
I stepped to the next box in the cluster and it works like a charm - go figure.

thank you however for a clear quick response -your a great asset to the community!
 

spirit

Famous Member
Apr 2, 2010
5,866
702
133
www.odiso.com
Is there by chance a "how to set mtu for dummies" guide?
I did some searching - found some perl code - in the forums - some referenced back to 1.x etc...
Sadly searching the forums since 2.x is out has been a bit more difficult

that being said here is what I need to figure out.

We have a cluster with 8 systems in it.
We want to have that cluster use our SAN.
Our SAN is set to an MTU of 9000 on its own ip range (not vlan just ip range)

What I would like to do in each system is setup so the vmbr0 operates at its normal 1500 MTU
and each system to have the eth1 network port to use the MTU of 9000

Anyhow - I think a For Dummies write up would be excellent for those trying to figure this out.

I you can mix differents mtu, always set same mtu on your ethX and vmbrX

so, you need dedicated network card for your san (mtu9000) and dedicated network card on your lan (mtu 1500).

For the config, simply set "MTU 9000" options to your san network card in /etc/network/interfaces
 

tom

Proxmox Staff Member
Staff member
Aug 29, 2006
15,619
959
163
there are a lot of NIC around which do not support with MTU 9000 (check specifications). if you expect high performance, go for high performance NIC cards. also the Switch must be enabled for MTU 9000.
 

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