mitchellh/vagrant — pull request #4439 by omehegan (2014-09-02 23:59:20+00:00)
Title: Note that the VirtualBox provider does not support --parallel.

I spent a day refactoring code to generate multi-machine Vagrantfiles, only to discover my time was wasted because the VirtualBox provider doesn't support --parallel. Would have been nice to know that before I started, so I added a note to the documentation in what seemed like the logical place.