Most hypervisors now have, or will have, support for SR-IOV networking — VMware introduced support in vSphere 5.1. One of the downsides of using this technology, which provides direct network access to a virtual machine, is that it hinders mobility — vMotion is no longer possible. The new Hyper-V works around this limitation by temporarily routing I/O through a virtual switch during live migration. Ingenious, no?
Over three years ago, VMware and partners demonstrated a solution to the SR-IOV/vMotion issue — by temporarily switching from passthrough to emulation mode it was possible to migrate a VM from one host to another. This innovation can be seen in the following demonstration:
Now, you may be asking why VMware never shipped this feature if it existed over three years ago. I’m not privvy to any specific details on the topic, but it would be sensible to say that decisions to release features are made based on priorities such as customer value. Although hardware with SR-IOV support is now becoming widely available, the customer use cases are still very much at the edges. Consider this: if a workload is so latency-sensitive that SR-IOV is truly required, how acceptable is it to impact service levels while I/O is rerouted during this migration period?
While this feature isn’t part of a shipping product from VMware, I’d argue that vSphere had it before Hyper-V for all intents and purposes. Especially considering the weight Microsoft gives to the capabilities of their pre-release software.
Happy New Year!