Add a second disk to system using vagrant

file_to_disk = './tmp/large_disk.vdi'

Vagrant::Config.run do |config|
  config.vm.box = 'base'

  config.vm.customize ['createhd', '--filename', file_to_disk, '--size', 500 * 1024]
  config.vm.customize ['storageattach', :id, '--storagectl', 'SATA Controller', '--port', 1, '--device', 0, '--type', 'hdd', '--medium', file_to_disk]
end

(see gist)