VDEV_LABEL_SPACE
asize = vdevsize - VDEV_LABEL_SPACE;
vdevsize1 = rounddown2(asize, mssize) + VDEV_LABEL_SPACE;
vdevsize1 = roundup2(asize, mssize) + VDEV_LABEL_SPACE;
asize = vdevsize - VDEV_LABEL_SPACE;
_Static_assert(VDEV_LABEL_SPACE <= MINDEVSIZE, "");