diff --git a/sys/cam/ata/ata_da.c b/sys/cam/ata/ata_da.c
index 396802656cdf..8a279311b4a3 100644
--- a/sys/cam/ata/ata_da.c
+++ b/sys/cam/ata/ata_da.c
@@ -874,7 +874,8 @@ adastart(struct cam_periph *periph, union ccb *start_ccb)
 		}
 		bioq_remove(&softc->bio_queue, bp);
 
-		if ((softc->flags & ADA_FLAG_NEED_OTAG) != 0) {
+		if ((bp->bio_flags & BIO_ORDERED) != 0
+		 || (softc->flags & ADA_FLAG_NEED_OTAG) != 0) {
 			softc->flags &= ~ADA_FLAG_NEED_OTAG;
 			softc->ordered_tag_count++;
 			tag_code = 0;
diff --git a/sys/cam/scsi/scsi_da.c b/sys/cam/scsi/scsi_da.c
index 8f643611c0cc..7729ecc5ef54 100644
--- a/sys/cam/scsi/scsi_da.c
+++ b/sys/cam/scsi/scsi_da.c
@@ -1354,7 +1354,8 @@ dastart(struct cam_periph *periph, union ccb *start_ccb)
 
 			bioq_remove(&softc->bio_queue, bp);
 
-			if ((softc->flags & DA_FLAG_NEED_OTAG) != 0) {
+			if ((bp->bio_flags & BIO_ORDERED) != 0
+			 || (softc->flags & DA_FLAG_NEED_OTAG) != 0) {
 				softc->flags &= ~DA_FLAG_NEED_OTAG;
 				softc->ordered_tag_count++;
 				tag_code = MSG_ORDERED_Q_TAG;
@@ -1368,7 +1369,8 @@ dastart(struct cam_periph *periph, union ccb *start_ccb)
 						/*retries*/da_retry_count,
 						/*cbfcnp*/dadone,
 						/*tag_action*/tag_code,
-						/*read_op*/bp->bio_cmd == BIO_READ,
+						/*read_op*/bp->bio_cmd
+							== BIO_READ,
 						/*byte2*/0,
 						softc->minimum_cmd_size,
 						/*lba*/bp->bio_pblkno,
@@ -1377,17 +1379,24 @@ dastart(struct cam_periph *periph, union ccb *start_ccb)
 						/*data_ptr*/ bp->bio_data,
 						/*dxfer_len*/ bp->bio_bcount,
 						/*sense_len*/SSD_FULL_SIZE,
-						/*timeout*/da_default_timeout*1000);
+						da_default_timeout * 1000);
 				break;
 			case BIO_FLUSH:
+				/*
+				 * BIO_FLUSH doesn't currently communicate
+				 * range data, so we synchronize the cache
+				 * over the whole disk.  We also force
+				 * ordered tag semantics the flush applies
+				 * to all previously queued I/O.
+				 */
 				scsi_synchronize_cache(&start_ccb->csio,
 						       /*retries*/1,
 						       /*cbfcnp*/dadone,
-						       MSG_SIMPLE_Q_TAG,
-						       /*begin_lba*/0,/* Cover the whole disk */
+						       MSG_ORDERED_Q_TAG,
+						       /*begin_lba*/0,
 						       /*lb_count*/0,
 						       SSD_FULL_SIZE,
-						       /*timeout*/da_default_timeout*1000);
+						       da_default_timeout*1000);
 				break;
 			}
 			start_ccb->ccb_h.ccb_state = DA_CCB_BUFFER_IO;
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c
index 00817bfef24b..d0d5137913c8 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c
@@ -598,6 +598,7 @@ vdev_geom_io_start(zio_t *zio)
 		break;
 	case ZIO_TYPE_IOCTL:
 		bp->bio_cmd = BIO_FLUSH;
+		bp->bio_flags |= BIO_ORDERED;
 		bp->bio_data = NULL;
 		bp->bio_offset = cp->provider->mediasize;
 		bp->bio_length = 0;
diff --git a/sys/geom/geom_io.c b/sys/geom/geom_io.c
index b145441cad75..b4044a75e33c 100644
--- a/sys/geom/geom_io.c
+++ b/sys/geom/geom_io.c
@@ -265,6 +265,7 @@ g_io_flush(struct g_consumer *cp)
 	g_trace(G_T_BIO, "bio_flush(%s)", cp->provider->name);
 	bp = g_alloc_bio();
 	bp->bio_cmd = BIO_FLUSH;
+	bp->bio_flags |= BIO_ORDERED;
 	bp->bio_done = NULL;
 	bp->bio_attribute = NULL;
 	bp->bio_offset = cp->provider->mediasize;
diff --git a/sys/geom/sched/subr_disk.c b/sys/geom/sched/subr_disk.c
index 008eaab1c94b..db2a9ef11f8c 100644
--- a/sys/geom/sched/subr_disk.c
+++ b/sys/geom/sched/subr_disk.c
@@ -86,7 +86,7 @@ __FBSDID("$FreeBSD$");
  * bioq_remove()	remove a generic element from the queue, act as
  *		bioq_takefirst() if invoked on the head of the queue.
  *
- * The semantic of these methods is the same of the operations
+ * The semantic of these methods is the same as the operations
  * on the underlying TAILQ, but with additional guarantees on
  * subsequent bioq_disksort() calls. E.g. bioq_insert_tail()
  * can be useful for making sure that all previous ops are flushed
@@ -115,10 +115,10 @@ void
 gs_bioq_remove(struct bio_queue_head *head, struct bio *bp)
 {
 
-	if (bp == TAILQ_FIRST(&head->queue))
-		head->last_offset = bp->bio_offset + bp->bio_length;
-
-	if (bp == head->insert_point)
+	if (head->insert_point == NULL) {
+		if (bp == TAILQ_FIRST(&head->queue))
+			head->last_offset = bp->bio_offset + bp->bio_length;
+	} else if (bp == head->insert_point)
 		head->insert_point = NULL;
 
 	TAILQ_REMOVE(&head->queue, bp, bio_queue);
@@ -137,7 +137,8 @@ void
 gs_bioq_insert_head(struct bio_queue_head *head, struct bio *bp)
 {
 
-	head->last_offset = bp->bio_offset;
+	if (head->insert_point == NULL)
+		head->last_offset = bp->bio_offset;
 	TAILQ_INSERT_HEAD(&head->queue, bp, bio_queue);
 }
 
@@ -147,6 +148,7 @@ gs_bioq_insert_tail(struct bio_queue_head *head, struct bio *bp)
 
 	TAILQ_INSERT_TAIL(&head->queue, bp, bio_queue);
 	head->insert_point = bp;
+	head->last_offset = bp->bio_offset;
 }
 
 struct bio *
@@ -189,13 +191,28 @@ gs_bioq_bio_key(struct bio_queue_head *head, struct bio *bp)
 void
 gs_bioq_disksort(struct bio_queue_head *head, struct bio *bp)
 {
-	struct bio *cur, *prev = NULL;
-	uoff_t key = gs_bioq_bio_key(head, bp);
+	struct bio *cur, *prev;
+	uoff_t key;
 
+	if ((bp->bio_flags & BIO_ORDERED) != 0) {
+		/*
+		 * Ordered transactions can only be dispatched
+		 * after any currently queued transactions.  They
+		 * also have barrier semantics - no transactions
+		 * queued in the future can pass them.
+		 */
+		gs_bioq_insert_tail(head, bp);
+		return;
+	}
+
+	prev = NULL;
+	key = gs_bioq_bio_key(head, bp);
 	cur = TAILQ_FIRST(&head->queue);
 
-	if (head->insert_point)
-		cur = head->insert_point;
+	if (head->insert_point) {
+		prev = head->insert_point;
+		cur = TAILQ_NEXT(head->insert_point, bio_queue);
+	}
 
 	while (cur != NULL && key >= gs_bioq_bio_key(head, cur)) {
 		prev = cur;
diff --git a/sys/kern/subr_disk.c b/sys/kern/subr_disk.c
index 12b015944c2a..23915402e30d 100644
--- a/sys/kern/subr_disk.c
+++ b/sys/kern/subr_disk.c
@@ -127,7 +127,7 @@ disk_err(struct bio *bp, const char *what, int blkdone, int nl)
  * bioq_remove()	remove a generic element from the queue, act as
  *		bioq_takefirst() if invoked on the head of the queue.
  *
- * The semantic of these methods is the same of the operations
+ * The semantic of these methods is the same as the operations
  * on the underlying TAILQ, but with additional guarantees on
  * subsequent bioq_disksort() calls. E.g. bioq_insert_tail()
  * can be useful for making sure that all previous ops are flushed
@@ -156,10 +156,10 @@ void
 bioq_remove(struct bio_queue_head *head, struct bio *bp)
 {
 
-	if (bp == TAILQ_FIRST(&head->queue))
-		head->last_offset = bp->bio_offset + bp->bio_length;
-
-	if (bp == head->insert_point)
+	if (head->insert_point == NULL) {
+		if (bp == TAILQ_FIRST(&head->queue))
+			head->last_offset = bp->bio_offset + bp->bio_length;
+	} else if (bp == head->insert_point)
 		head->insert_point = NULL;
 
 	TAILQ_REMOVE(&head->queue, bp, bio_queue);
@@ -178,7 +178,8 @@ void
 bioq_insert_head(struct bio_queue_head *head, struct bio *bp)
 {
 
-	head->last_offset = bp->bio_offset;
+	if (head->insert_point == NULL)
+		head->last_offset = bp->bio_offset;
 	TAILQ_INSERT_HEAD(&head->queue, bp, bio_queue);
 }
 
@@ -188,6 +189,7 @@ bioq_insert_tail(struct bio_queue_head *head, struct bio *bp)
 
 	TAILQ_INSERT_TAIL(&head->queue, bp, bio_queue);
 	head->insert_point = bp;
+	head->last_offset = bp->bio_offset;
 }
 
 struct bio *
@@ -230,13 +232,28 @@ bioq_bio_key(struct bio_queue_head *head, struct bio *bp)
 void
 bioq_disksort(struct bio_queue_head *head, struct bio *bp)
 {
-	struct bio *cur, *prev = NULL;
-	uoff_t key = bioq_bio_key(head, bp);
+	struct bio *cur, *prev;
+	uoff_t key;
 
+	if ((bp->bio_flags & BIO_ORDERED) != 0) {
+		/*
+		 * Ordered transactions can only be dispatched
+		 * after any currently queued transactions.  They
+		 * also have barrier semantics - no transactions
+		 * queued in the future can pass them.
+		 */
+		bioq_insert_tail(head, bp);
+		return;
+	}
+
+	prev = NULL;
+	key = bioq_bio_key(head, bp);
 	cur = TAILQ_FIRST(&head->queue);
 
-	if (head->insert_point)
-		cur = head->insert_point;
+	if (head->insert_point) {
+		prev = head->insert_point;
+		cur = TAILQ_NEXT(head->insert_point, bio_queue);
+	}
 
 	while (cur != NULL && key >= bioq_bio_key(head, cur)) {
 		prev = cur;
diff --git a/sys/sys/bio.h b/sys/sys/bio.h
index 8b6ff0ec696a..c016ee67b904 100644
--- a/sys/sys/bio.h
+++ b/sys/sys/bio.h
@@ -54,6 +54,7 @@
 #define BIO_ERROR	0x01
 #define BIO_DONE	0x02
 #define BIO_ONQUEUE	0x04
+#define BIO_ORDERED	0x08
 
 #ifdef _KERNEL
 struct disk;