expandable RAID-Z

@@ -553,8 +553,9 @@
         vdev_disk_probe,
         vdev_default_asize,
         vdev_disk_io_start,
         vdev_disk_io_done,
         NULL,
+        NULL,
         VDEV_TYPE_DISK,         /* name of this vdev type */
         B_TRUE                  /* leaf vdev */
 };