vdev_uberblock_compare
if (vdev_uberblock_compare(buf, ub) > 0)
vdev_uberblock_compare(ubbest, &(current_uberblock)) <= 0))
vdev_uberblock_compare(ubnext, ubbest) > 0)
vdev_uberblock_compare(ub, cbp->ubl_ubbest) > 0) {