Enabling jumbo frames ESX 4.1

[pdrace]

I've read the KB article on enabling jumbo frames and I am confused.

I have an existing vswitches on two ESX 4.1 hosts that are used for IP storage that I want to enable jumbo frames on.

The Vcenter server they are connected to is running 5.0 update 1.

I understand that I have to enable the vswitch for jumbo frames with the esxcfg-vswitch command and set the mtu for the portgroup.

It appears the mtu on the switch and portgroups can be set through Vcenter with Vcenter 5. Is there any reason to do this at the command line since my  hosts are managed through a Vcenter 5 server? 

[a_p_ · Accepted solution]

If the option to set the MTU on the vSwitch and port groups is available, there's no need to do this on the command line. Actually, I was not aware of this and thought this was only available with the hosts also being version 5.

What I recommend anyway is to test whether Jumbo frames work end-to-end after setting things up. To do this run

vmkping -s 8972 -d <iSCSI-Target-IP>

to make sure the frames are not segmented. For an interesting explanation about this see http://rickardnobel.se/archives/992

André

[pdrace]

I'll let you know if it works. I ran into more basic issues.

I couldn't remove the existing port groups in Vcenter or from the command line on the two hosts.

I deleted the vswitches and recreated them but then couldn't add a vmkernel port to the switches.

Spent two hours on the phone with VMWare tech support. They managed to get a vmkernel port added to one of them but gave up on the other and told me the easiest solution was to reinstall. I'll try setting the mtu on the switches and ports after I'm done reinstalling the second host.

[rickardnobel]

Parker Race wrote:

I'll try setting the mtu on the switches and ports after I'm done reinstalling the second host.

Remember to create the Vmkernel vmknic from the commandline and set the MTU at the same time, as this unfortunately could not be changed later on 4.x.

[a_p_]

That's what I thought too, before a came across http://kb.vmware.com/kb/1007654

With ESXi 4.1 it is possible to modify the MTU for already existing port groups.

One thing in the KB that didn't work for me was:

Note: If you plan to have a vSwitch which just contains the iSCSI  port group you can specify the MTU for the vSwitch to be 9000 and not  specify the MTU when creating the vmkernel port in the next step.

Without specifying the MTU on the port group, Jumbo frames didn't work.

André

[rickardnobel]

André Pett wrote:

That's what I thought too, before a came across http://kb.vmware.com/kb/1007654

With ESXi 4.1 it is possible to modify the MTU for already existing port groups.

One thing in the KB that didn't work for me was:

Note: If you plan to have a vSwitch which just contains the iSCSI  port group you can specify the MTU for the vSwitch to be 9000 and not  specify the MTU when creating the vmkernel port in the next step.

Without specifying the MTU on the port group, Jumbo frames didn't work.

Hello André, very interesting and still a bit strange. I can remember wrong, but I think I have failed to set the MTU on an existing vmknic port. I shall see if I can verify this on 4.1.

It should be good if it was correct that a vmknic should inherit the MTU setting of the vSwitch.

[rickardnobel]

I have done some short tests now for the inheritance of MTU from vSwitch to Vmkernel port.

If having a vSwitch created (with either GUI or CLI) and then set to 9000 MTU, and after that created Vmkernel ports (both from GUI and CLI) and in both cases the MTU of the new vmkernel port was set to default 1500. (Verifed with esxcfg-vmknic -l)

The good news was that it did work with using the following on an existing vmknic:

esxcfg-vmknic -m 9000 vmk-test-2

So the inability to change MTU on an already created vmkernel port seem to been lifted between 4.0 and 4.1.

[pdrace]

I was able to set the MTU on the port group as well as the switch in Vcenter on the hosts but haven't had time to test the configuration yet.

[pdrace]

I set the mtu on the switches on the hosts to 9000. This did not change the port groups, they remained 1500.

I was able to change the port group mtus to 9000 in the vcenter GUI and have now successfully tested using vmkping -2 8972 -d IP address.