Jumbo frame and VM with 1500 MTU size : performance impact ?

[mldmld]

Hi all,

I'm deploying ESXi 4.1U1 or U2, and my network manager suggests to enable jumbo frame. I think it's a good idea :smileycool:

I read the Vmware documentation and it says that every component on the network must be set with a MTU = 9000

We have VMs with legacy networking. So to enable Jumbo frame  at VM level, documentation says I must install a vmxnet adapter. So it needs to stop the service of each VM. As I have hundreds of VM, it's not possible. To much time to spend to negociate a VM shutdown with each customer.

So if

- I set MTU to 9000 at vSwitch and vmkernel level

- I install new VM with vmxnet nic with jumbo frame enabled and set the MTU to 9000 at OS guest level too

- Let the old VM with their MTU set to 1500

Would the old VM see their performance decrease ?

Thanks for your help

Best regards

[VMmatty]

The VMs that still have the old adapter should not experience any change.  As stated if everything in the path is not configured to use Jumbo Frames then it just negotiates down to the smaller MTU size.  I would not expect any performance degredation on your older VMs.

On the flip side, I would not expect a major performance increase on those guests with Jumbo Frames enabled.  Jumbo Frames can help improve performance in certain situations but not in all.  It can definitely help improve performance in areas like vMotion or iSCSI storage but it may not help your applications.

I would do some testing to see if it helps your particular application(s) and go from there.  But I wouldn't go into it expecting major performance improvements just by enabling Jumbo Frames.

Matt

http://www.thelowercasew.com