mtu 9000 on vSwitch?

[mlubinski]

Hi,

i have 2 clusters connected to netapp storage. first cluster (all hosts) have vSwitch 2 connected to storage, and it has MTU set to 9000. However second cluster has vSwitch2 set MTU to 1500 (default).

As I before got information from VMware MTU size 9000 is not supported by VMware for version 3.5. How do you think, should I change mtu size for all servers in second cluster to 9000 as the first server, or should I leave it default? Should this have any storage performance impact on current storage?

Switch Name Num Ports Used Ports Configured Ports MTU Uplinks

vSwitch2 64 4 64 1500 vmnic2

what does this MTU to the storage? bigger value makes bigger performance?

[AndreTheGiant]

Jumbo frame can increase performance using bigger packets.

But as you say in ESX 3.5 are not supported for storage traffic on vmkernel interfaces.

You can increase MTU on switches (this is supported), but you have to decide if you want also increse the MTU on vmkernel interfaces.

In my labs I use Jumbo Frame in ESX 3.5 and with iSCSI traffic with no problem.

Andre

[VMmatty]

If you are connecting that NetApp SAN to the ESX hosts for VMFS storage, then I agree with Andre that you probably shouldn't configure Jumbo Frames since they are not supported for storage traffic. If you are connecting virtual machines to iSCSI volumes by using the Software Initiator inside the VM, then you can enable Jumbo Frames and still be supported. Both configurations will work but only one is truly supported by VMware in ESX 3.5. I haven't seen much of a performance difference using Jumbo Frames in either configuration, for whatever that's worth.

[mlubinski]

thx for your replies. we use netapp with nfs for our vmware environment.

just to be sure, if on these default servers I will run command esxcfg-vswitch -m 9000 vSwitch2, then automatically this host will be using Jumbo frames? should it be rebooted after it? or maybe should there be any other command for this?

[VMmatty]

You'll need to execute that command in order to enable Jumbo Frames on the vSwitch. Then you'll need to create a VMkernel portgroup with the MTU set to 9000 using a command similar to the following:

esxcfg-vmknic -a -i <ip address> -n <subnet mask> -m 9000 <name of portgroup>

So for example it would look like this:

esxcfg-vmknic -a -i 10.1.10.10 -m 255.255.255.0 -m 9000 nfs_storage

See the following for a more detailed description:

[mlubinski]

ok and what if this vmknic is already configured? should I just type this command with current ip and netmask but with 9000 mtu? is it enough?

[VMmatty]

I think you need to recreate the VMkernel portgroup first if you want to set the MTU. I don't think you can apply that change to an existing VMkernel portgroup.

[AndreTheGiant · Accepted solution]

ok and what if this vmknic is already configured? should I just type this command with current ip and netmask but with 9000 mtu? is it enough?

The only way is create a new vmkernel interface and delete the old one.

Andre

[mlubinski]

ok, thanks guys for your answer. Now it is clear for me.