diff --git a/man/man5/zfs-module-parameters.5 b/man/man5/zfs-module-parameters.5
index f4afe2525..888c70730 100644
--- a/man/man5/zfs-module-parameters.5
+++ b/man/man5/zfs-module-parameters.5
@@ -3326,7 +3326,7 @@ Default value: \fB0\fR.
 Maximum amount of data that can be concurrently issued at once for scrubs and
 resilvers per leaf device, given in bytes.
 .sp
-Default value: \fB41943040\fR.
+Default value: \fB4194304\fR.
 .RE
 
 .sp
diff --git a/module/zfs/dsl_scan.c b/module/zfs/dsl_scan.c
index cc1cbcdb9..62ee9bb9a 100644
--- a/module/zfs/dsl_scan.c
+++ b/module/zfs/dsl_scan.c
@@ -126,7 +126,7 @@ static boolean_t scan_ds_queue_contains(dsl_scan_t *scn, uint64_t dsobj,
 static void scan_ds_queue_insert(dsl_scan_t *scn, uint64_t dsobj, uint64_t txg);
 static void scan_ds_queue_remove(dsl_scan_t *scn, uint64_t dsobj);
 static void scan_ds_queue_sync(dsl_scan_t *scn, dmu_tx_t *tx);
-static uint64_t dsl_scan_count_leaves(vdev_t *vd);
+static uint64_t dsl_scan_count_data_disks(vdev_t *vd);
 
 extern int zfs_vdev_async_write_active_min_dirty_percent;
 
@@ -451,7 +451,7 @@ dsl_scan_init(dsl_pool_t *dp, uint64_t txg)
 	 * phase are done per top-level vdev and are handled separately.
 	 */
 	scn->scn_maxinflight_bytes = MAX(zfs_scan_vdev_limit *
-	    dsl_scan_count_leaves(spa->spa_root_vdev), 1ULL << 20);
+	    dsl_scan_count_data_disks(spa->spa_root_vdev), 1ULL << 20);
 
 	avl_create(&scn->scn_queue, scan_ds_queue_compare, sizeof (scan_ds_t),
 	    offsetof(scan_ds_t, sds_node));
@@ -2759,22 +2759,16 @@ dsl_scan_visit(dsl_scan_t *scn, dmu_tx_t *tx)
 }
 
 static uint64_t
-dsl_scan_count_leaves(vdev_t *vd)
+dsl_scan_count_data_disks(vdev_t *rvd)
 {
 	uint64_t i, leaves = 0;
 
-	/* we only count leaves that belong to the main pool and are readable */
-	if (vd->vdev_islog || vd->vdev_isspare ||
-	    vd->vdev_isl2cache || !vdev_readable(vd))
-		return (0);
-
-	if (vd->vdev_ops->vdev_op_leaf)
-		return (1);
-
-	for (i = 0; i < vd->vdev_children; i++) {
-		leaves += dsl_scan_count_leaves(vd->vdev_child[i]);
+	for (i = 0; i < rvd->vdev_children; i++) {
+		vdev_t *vd = rvd->vdev_child[i];
+		if (vd->vdev_islog || vd->vdev_isspare || vd->vdev_isl2cache)
+			continue;
+		leaves += vdev_get_ndisks(vd) - vdev_get_nparity(vd);
 	}
-
 	return (leaves);
 }
 
@@ -3017,8 +3011,6 @@ scan_io_queues_run_one(void *arg)
 	range_seg_t *rs = NULL;
 	scan_io_t *sio = NULL;
 	list_t sio_list;
-	uint64_t bytes_per_leaf = zfs_scan_vdev_limit;
-	uint64_t nr_leaves = dsl_scan_count_leaves(queue->q_vd);
 
 	ASSERT(queue->q_scn->scn_is_sorted);
 
@@ -3026,9 +3018,9 @@ scan_io_queues_run_one(void *arg)
 	    offsetof(scan_io_t, sio_nodes.sio_list_node));
 	mutex_enter(q_lock);
 
-	/* calculate maximum in-flight bytes for this txg (min 1MB) */
-	queue->q_maxinflight_bytes =
-	    MAX(nr_leaves * bytes_per_leaf, 1ULL << 20);
+	/* Calculate maximum in-flight bytes for this vdev. */
+	queue->q_maxinflight_bytes = MAX(1, zfs_scan_vdev_limit *
+	    (vdev_get_ndisks(queue->q_vd) - vdev_get_nparity(queue->q_vd)));
 
 	/* reset per-queue scan statistics for this txg */
 	queue->q_total_seg_size_this_txg = 0;
@@ -3665,16 +3657,14 @@ dsl_scan_sync(dsl_pool_t *dp, dmu_tx_t *tx)
 		/* Need to scan metadata for more blocks to scrub */
 		dsl_scan_phys_t *scnp = &scn->scn_phys;
 		taskqid_t prefetch_tqid;
-		uint64_t bytes_per_leaf = zfs_scan_vdev_limit;
-		uint64_t nr_leaves = dsl_scan_count_leaves(spa->spa_root_vdev);
 
 		/*
 		 * Recalculate the max number of in-flight bytes for pool-wide
 		 * scanning operations (minimum 1MB). Limits for the issuing
 		 * phase are done per top-level vdev and are handled separately.
 		 */
-		scn->scn_maxinflight_bytes =
-		    MAX(nr_leaves * bytes_per_leaf, 1ULL << 20);
+		scn->scn_maxinflight_bytes = MAX(zfs_scan_vdev_limit *
+		    dsl_scan_count_data_disks(spa->spa_root_vdev), 1ULL << 20);
 
 		if (scnp->scn_ddt_bookmark.ddb_class <=
 		    scnp->scn_ddt_class_max) {
@@ -4050,9 +4040,8 @@ scan_exec_io(dsl_pool_t *dp, const blkptr_t *bp, int zio_flags,
 	size_t size = BP_GET_PSIZE(bp);
 	abd_t *data = abd_alloc_for_io(size, B_FALSE);
 
-	ASSERT3U(scn->scn_maxinflight_bytes, >, 0);
-
 	if (queue == NULL) {
+		ASSERT3U(scn->scn_maxinflight_bytes, >, 0);
 		mutex_enter(&spa->spa_scrub_lock);
 		while (spa->spa_scrub_inflight >= scn->scn_maxinflight_bytes)
 			cv_wait(&spa->spa_scrub_io_cv, &spa->spa_scrub_lock);
@@ -4061,6 +4050,7 @@ scan_exec_io(dsl_pool_t *dp, const blkptr_t *bp, int zio_flags,
 	} else {
 		kmutex_t *q_lock = &queue->q_vd->vdev_scan_io_queue_lock;
 
+		ASSERT3U(queue->q_maxinflight_bytes, >, 0);
 		mutex_enter(q_lock);
 		while (queue->q_inflight_bytes >= queue->q_maxinflight_bytes)
 			cv_wait(&queue->q_zio_cv, q_lock);