VagrantでVM起動時に、追加ディスクを作成してアタッチ - VirtualBox Provider ref: http://qiita.com/sawanoboly/items/cbd056252a130a4b961e

file1.txt

VBoxManage storageattach    <uuid|vmname>
                            --storagectl <name>
                            [--port <number>]
                            [--device <number>]
                            [--type dvddrive|hdd|fdd]
                            [--medium none|emptydrive|additions|
                                      <uuid|filename>|host:<drive>|iscsi]
                            [--mtype normal|writethrough|immutable|shareable|
                                     readonly|multiattach]
                            [--comment <text>]
                            [--setuuid <uuid>]
                            [--setparentuuid <uuid>]
                            [--passthrough on|off]
                            [--tempeject on|off]
                            [--nonrotational on|off]
                            [--discard on|off]
                            [--bandwidthgroup <name>]
                            [--forceunmount]
                            [--server <name>|<ip>]
                            [--target <target>]
                            [--tport <port>]
                            [--lun <lun>]
                            [--encodedlun <lun>]
                            [--username <username>]
                            [--password <password>]
                            [--initiator <initiator>]
                            [--intnet]

Vagrantfile

# -- snip --
    config.vm.define machine do |config|

      config.vm.provider :virtualbox do |vb|
        at_disk = 'tmp/name_of_file.vdi'
        unless File.exists?(at_disk)
          vb.customize ['createhd', '--filename', at_disk, '--size', 5 * 1024]
        end
        vb.customize ['storageattach', :id, '--storagectl', 'IDE Controller', '--port', 1, '--device', 0, '--type', 'hdd', '--medium', at_disk]
        end
      end

    end
# -- snip --