UBERBLOCK_SHIFT
MIN(MAX((vd)->v_top->v_ashift, UBERBLOCK_SHIFT), MAX_UBERBLOCK_SHIFT)
#define MAX_UBERBLOCK_COUNT (VDEV_UBERBLOCK_RING >> UBERBLOCK_SHIFT)
MAX((sh), UBERBLOCK_SHIFT)
MIN(MAX((vd)->vdev_top->vdev_ashift, UBERBLOCK_SHIFT), \