def DiskName(vm_name, disk_type, disk_number):
  """Returns the name of this disk.

  Args:
    vm_name: The name of the vm this disk will be attached to.
    disk_type: The type of the disk.
    disk_number: The number of this disk. Must be unique on the VM.

  Returns:
    The name of the disk.
  """
  return "{}-disk-{}-{}".format(vm_name, disk_type, disk_number)