Index: sys/geom/mirror/g_mirror.c
===================================================================
--- sys/geom/mirror/g_mirror.c	(revision 195748)
+++ sys/geom/mirror/g_mirror.c	(working copy)
@@ -45,7 +45,6 @@
 #include <sys/sched.h>
 #include <geom/mirror/g_mirror.h>
 
-
 static MALLOC_DEFINE(M_MIRROR, "mirror_data", "GEOM_MIRROR Data");
 
 SYSCTL_DECL(_kern_geom);
@@ -71,7 +70,12 @@
 TUNABLE_INT("kern.geom.mirror.sync_requests", &g_mirror_syncreqs);
 SYSCTL_UINT(_kern_geom_mirror, OID_AUTO, sync_requests, CTLFLAG_RDTUN,
     &g_mirror_syncreqs, 0, "Parallel synchronization I/O requests.");
+static u_int g_mirror_plusdelay = 60000;
+TUNABLE_INT("kern.geom.mirror.plusdelay", &g_mirror_plusdelay);
+SYSCTL_UINT(_kern_geom_mirror, OID_AUTO, plusdelay, CTLFLAG_RW,
+    &g_mirror_plusdelay, 0, "Additional load delay in 1/65536ths of a second.");
 
+
 #define	MSLEEP(ident, mtx, priority, wmesg, timeout)	do {		\
 	G_MIRROR_DEBUG(4, "%s: Sleeping %p.", __func__, (ident));	\
 	msleep((ident), (mtx), (priority), (wmesg), (timeout));		\
@@ -451,8 +455,7 @@
 	disk->d_id = md->md_did;
 	disk->d_state = G_MIRROR_DISK_STATE_NONE;
 	disk->d_priority = md->md_priority;
-	disk->d_delay.sec = 0;
-	disk->d_delay.frac = 0;
+	disk->last_offset = 0;
 	binuptime(&disk->d_last_used);
 	disk->d_flags = md->md_dflags;
 	if (md->md_provider[0] != '\0')
@@ -863,16 +866,6 @@
 }
 
 static void
-g_mirror_update_delay(struct g_mirror_disk *disk, struct bio *bp)
-{
-
-	if (disk->d_softc->sc_balance != G_MIRROR_BALANCE_LOAD)
-		return;
-	binuptime(&disk->d_delay);
-	bintime_sub(&disk->d_delay, &bp->bio_t0);
-}
-
-static void
 g_mirror_done(struct bio *bp)
 {
 	struct g_mirror_softc *sc;
@@ -904,8 +897,6 @@
 		g_topology_lock();
 		g_mirror_kill_consumer(sc, bp->bio_from);
 		g_topology_unlock();
-	} else {
-		g_mirror_update_delay(disk, bp);
 	}
 
 	pbp->bio_inbed++;
@@ -1472,25 +1463,49 @@
 	struct g_consumer *cp;
 	struct bio *cbp;
 	struct bintime curtime;
+	off_t  bio_offset;
+	off_t  best_dist, dist;
+	uint64_t best_use_delay, use_delay;
 
-	binuptime(&curtime);
+	bio_offset = bp->bio_offset;
+	best_dist = -1;
+	best_use_delay = use_delay = 0;
+
+	getbinuptime(&curtime);
 	/*
-	 * Find a disk which the smallest load.
+	 * Find the disk which has the smallest ratio of distance to use
+	 * delay, i.e. its head looks closest to bio_offset and it was used
+	 * least recently.
 	 */
 	disk = NULL;
 	LIST_FOREACH(dp, &sc->sc_disks, d_next) {
 		if (dp->d_state != G_MIRROR_DISK_STATE_ACTIVE)
 			continue;
-		/* If disk wasn't used for more than 2 sec, use it. */
-		if (curtime.sec - dp->d_last_used.sec >= 2) {
+
+		dist = dp->last_offset - bio_offset;
+		if (dist < 0)
+			dist = -dist;
+
+		/*
+		 * Calculate the use delay as follows: Add the sysctl
+		 * configured delay, then convert the bintime structure
+		 * in terms of 1/65536ths of a second before adding its
+		 * components.  So multiply seconds difference by 65536
+		 * and drop all but the 16 most significant bits in the
+		 * fraction, since they're all greater than 1/65536.
+		 */
+		use_delay = g_mirror_plusdelay;
+		use_delay += ((curtime.sec - dp->d_last_used.sec) << 16);
+		use_delay += ((curtime.frac - dp->d_last_used.frac) >> 48);
+
+		if (best_dist == -1 ||
+		    dist * best_use_delay < best_dist * use_delay) {
 			disk = dp;
-			break;
+			best_dist = dist;
+			best_use_delay = use_delay;
 		}
-		if (disk == NULL ||
-		    bintime_cmp(&dp->d_delay, &disk->d_delay) < 0) {
-			disk = dp;
-		}
 	}
+
 	KASSERT(disk != NULL, ("NULL disk for %s.", sc->sc_name));
 	cbp = g_clone_bio(bp);
 	if (cbp == NULL) {
@@ -1505,7 +1520,8 @@
 	cp = disk->d_consumer;
 	cbp->bio_done = g_mirror_done;
 	cbp->bio_to = cp->provider;
-	binuptime(&disk->d_last_used);
+	disk->d_last_used = curtime;
+	disk->last_offset = bio_offset;
 	G_MIRROR_LOGREQ(3, cbp, "Sending request.");
 	KASSERT(cp->acr >= 1 && cp->acw >= 1 && cp->ace >= 1,
 	    ("Consumer %s not opened (r%dw%de%d).", cp->provider->name, cp->acr,
@@ -1659,6 +1675,7 @@
 				g_io_deliver(bp, bp->bio_error);
 				return;
 			}
+			disk->last_offset = bp->bio_offset;
 			bioq_insert_tail(&queue, cbp);
 			cbp->bio_done = g_mirror_done;
 			cp = disk->d_consumer;
Index: sys/geom/mirror/g_mirror.h
===================================================================
--- sys/geom/mirror/g_mirror.h	(revision 195748)
+++ sys/geom/mirror/g_mirror.h	(working copy)
@@ -133,7 +133,7 @@
 	struct g_mirror_softc	*d_softc; /* Back-pointer to softc. */
 	int		 d_state;	/* Disk state. */
 	u_int		 d_priority;	/* Disk priority. */
-	struct bintime	 d_delay;	/* Disk delay. */
+	off_t		 last_offset;	/* LBA of last operation. */
 	struct bintime	 d_last_used;	/* When disk was last used. */
 	uint64_t	 d_flags;	/* Additional flags. */
 	u_int		 d_genid;	/* Disk's generation ID. */