As I was preparing a presentation on Hyper-V cluster high available & high performance networking by, you guessed it, presenting it. During that presentation I mentioned Jumbo Frames & VMQ (VMDq in Intel speak)  for the virtual machine, Live Migration and CSV network. Jumbo frames are rather well know nowadays but VMQ is still something people have read about, at best have tinkered with, but no many are using it in production.

One of the reason for this that it isn’t explained and documented very well. You can find some decent explanation on what it is and does for you but that’s about it. The implementation information is woefully inadequate and, as with many advanced network features, there are many hiccups and intricacies. But that’s a subject for another blog post. I need some more input from Intel and or MSFT before I can finish that one.

Someone stated/asked that they knew that Jumbo frames are good for throughput on iSCSI networks and as such would also be beneficial to iSCSI networks provided to the virtual machines. But how about VMQ? Does that do anything at all for IP based storage. Yes it does. As a matter of fact It’s highly recommend by MSFT IT in one of their TechEd 2010 USA presentations on Hyper-V and storage.

So yes enable VMQ on both NIC ports used for iSCSI to the guest. Ideally these are two dedicated NICs connected to two separate switches to avoid a single point of failure. You do not need to team these on the host or have Multiple Path I/O (MPIO) running for this mat the parent level. The MPIO part is done in the virtual machines guests themselves as that’s where the iSCSI initiator lives with direct connect. And to address the question that followed, you can also use Multiple Connections per Session (MCS) in the guest if your storage device supports this but I must admit I have not seen this used in the wild. And then, finally coming to the point, both MPIO and MCS work transparently with Jumbo Frames and VMQ. So you’re good to go