Function vdev_set_deflate_ratio

freebsd/contrib/openzfs/module/zfs/vdev.c:1730–1737

* Compute the raidz-deflation ratio. Note, we hard-code * in 128k (1 << 17) because it is the "typical" blocksize. * Even though SPA_MAXBLOCKSIZE changed, this algorithm can not change, * otherwise it would inconsistently account for existing bp's. */

 * otherwise it would inconsistently account for existing bp's.
 */
static void
vdev_set_deflate_ratio(vdev_t *vd)
{
	if (vd == vd->vdev_top && !vd->vdev_ishole && vd->vdev_ashift != 0) {
		vd->vdev_deflate_ratio = (1 << 17) /
		    (vdev_psize_to_asize(vd, 1 << 17) >> SPA_MINBLOCKSHIFT);
	}
}

/*
 * Maximize performance by inflating the configured ashift for top level