Yep, vmotion's explicit arp wins in that regard, whereas as I suggest Xen requires tweaks in order to function optimally.

Such is the state of affairs with open source. I've been using Kemari in production for almost six months now. Some research prototypes are quite production-environment friendly.

Sounds like a delay on the switch. Add a gratuitous arp using arping in whatever vif-* script you're employing for virtual machine network interfaces and that problem will disappear.

Xen live migration does not involve 'continuous memory snapshotting' -- the referenced Kemari utilizes a combination of i/o triggers and observation of shadow page tables (nested page tables, ideally, if the hardware supports it. AMD's RVI and Intel's EPT). Kemari's equivalent of a lockstep vm gets only hot updates on dirtied pages, not a full memory snapshot. The alternative would of course be a rather inefficient design.

Instantly? Of course not. But the time required is equivalent to vmotion/live migration in bog-standard virtualization. How long? "That depends." To throw numbers at you, 30-100ms -- variance largely dependent upon how quickly your network infrastructure can react to MACs changing locations, whether in-flight TCP streams are broken as a result, etc. To help switches cope, people usually send a gratuitous ARP to jumpstart the process.

Check out the Kemari and Remus projects, which allow precisely the same in Xen environments. In essence, it's a continual live migration (vmware people, think continual vmotion) that resumes virtual machine execution on the backup node if the origin node dies. Very cool tech. The demonstration involved pulling the plug on one of the nodes. For more information just search, there are code and papers and presentation slides galore.

Bringing audio and/or transcript to silent films is also where such technology is applicable. An excellent documentary about computerized lip reading to accomplish the very same may be found via google video : http://video.google.com/videoplay?docid=189608705425991617&hl=en . I know it's quite early for an indirect invocation of Godwin's Law, but the documentary content is nevertheless quite related to this topic. It is entitled "Hitler Speaks" in reference to silent videos filmed in Hitler's presence.