vdev_create
spa->spa_root_vdev = vdev_create(guid, NULL);
vdev = vdev_create(guid, vdev_mirror_read);
vdev = vdev_create(guid, vdev_raidz_read);
vdev = vdev_create(guid, vdev_replacing_read);
vdev = vdev_create(guid, vdev_indirect_read);
vdev = vdev_create(guid, vdev_missing_read);
vdev = vdev_create(guid, vdev_disk_read);