NServiceBus is a very different technology than biz talk, I wouldn't call it Middleware.
It basically a message based event driven transport layer. By its very nature it's extremely easy to scale horizontally.
It basically a message based event driven transport layer. By its very nature it's extremely easy to scale horizontally.
For HA you simply run a distributor process for each logical event on windows cluster and add as many worker nodes as you see fit.
Because NServiceBus uses the store and forward pattern if a NServiceBus process/machine hosting it goes down, you are still guaranteed the eventual delivery of messages when the process/machine is resumed.