zpool iostat tells which rotor vector each vdev is part of.

For the time being, abusing the -S flag.

cmd/zpool/zpool_main.c

@@ -2804,6 +2804,8 @@ print_iostat_dashes(iostat_cbdata_t *cb, unsigned int force_column_width,
 
 	if (cb->cb_nonrotational)
 		printf("  -");
+	if (!(cb->cb_flags & IOS_ANYHISTO_M))
+		printf("  -");
 
 	/* For each bit in flags */
 	for (f = flags; f; f &= ~(1ULL << idx)) {
@@ -2863,17 +2865,22 @@ print_iostat_header_impl(iostat_cbdata_t *cb, unsigned int force_column_width,
 	else
 		printf("%*s", namewidth, "");
 
-
 	if (cb->cb_nonrotational)
 		printf("  N");
 
+	if (cb->cb_nonrotational)
+		printf("  R");
+
 	print_iostat_labels(cb, force_column_width, iostat_top_labels);
 
 	printf("%-*s", namewidth, title);
 
 	if (cb->cb_nonrotational)
 		printf("  R");
 
+	if (cb->cb_nonrotational)
+		printf("  V");
+
 	print_iostat_labels(cb, force_column_width, iostat_bottom_labels);
 
 	print_iostat_separator_impl(cb, force_column_width);
@@ -3377,6 +3384,12 @@ print_vdev_stats(zpool_handle_t *zhp, const char *name, nvlist_t *oldnv,
 			printf("%s%s", cb->cb_scripted ? "\t" : "  ",
 			    nonrotational_mark(newvs));
 		}
+		if (cb->cb_nonrotational) {
+			if (newvs->vs_nrotor != (uint64_t) -1)
+				(void) printf("  %d", (int) newvs->vs_nrotor);
+			else
+				(void) printf("  -");
+		}
 	}
 
 	/* Calculate our scaling factor */

include/sys/fs/zfs.h

@@ -826,6 +826,7 @@ typedef struct vdev_stat {
 	uint64_t	vs_state;		/* vdev state		*/
 	uint64_t	vs_aux;			/* see vdev_aux_t	*/
 	uint64_t	vs_nonrotational;	/* nonrotational	*/
+	uint64_t	vs_nrotor;		/* allocation rotor	*/
 	uint64_t	vs_alloc;		/* space allocated	*/
 	uint64_t	vs_space;		/* total capacity	*/
 	uint64_t	vs_dspace;		/* deflated capacity	*/

module/zfs/vdev.c

@@ -2930,6 +2930,10 @@ vdev_get_stats_ex(vdev_t *vd, vdev_stat_t *vs, vdev_stat_ex_t *vsx)
 			vs->vs_nonrotational = VDEV_NONROTATIONAL_MIXED;
 		else
 			vs->vs_nonrotational = VDEV_NONROTATIONAL_NO;
+		if (vd->vdev_mg)
+			vs->vs_nrotor = vd->vdev_mg->mg_nrot;
+		else
+			vs->vs_nrotor = -1;
 	}
 
 	ASSERT(spa_config_held(vd->vdev_spa, SCL_ALL, RW_READER) != 0);