This article assumes a KVM guest that runs from raw or qcow2 devices using emulated ide access. Since some time now, full virtualisation for block devices is available, facilitating the benefit of paravirtualisation. Benchmarked in bonnie++, the difference looks like this, revealing a way better performance of virtio:
Packer is a tool for creating identical machine images for multiple platforms from a single source configuration.
This is a Vagrant 1.1+ plugin that adds an Libvirt provider to Vagrant, allowing Vagrant to control and provision machines via Libvirt toolkit.