expandable RAID-Z

*** 89,96 ****
--- 89,97 ----
          vdev_missing_probe,
          vdev_default_asize,
          vdev_missing_io_start,
          vdev_missing_io_done,
          NULL,
+         NULL,
          VDEV_TYPE_MISSING,      /* name of this vdev type */
          B_TRUE                  /* leaf vdev */
  };