vdev_dtl_load
extern int vdev_dtl_load(vdev_t *vd);
if ((error = vdev_dtl_load(vd)) != 0 ||
error = vdev_dtl_load(vd->vdev_child[c]);
if (vd->vdev_ops->vdev_op_leaf && (error = vdev_dtl_load(vd)) != 0) {