Index: head/lib/libstand/stand.h
===================================================================
--- head/lib/libstand/stand.h
+++ head/lib/libstand/stand.h
@@ -194,6 +194,9 @@
 #define	F_WRITE		0x0002	/* file opened for writing */
 #define	F_RAW		0x0004	/* raw device open - no file system */
 #define F_NODEV		0x0008	/* network open - no device */
+#define	F_MASK		0xFFFF
+/* Mode modifier for strategy() */
+#define	F_NORA		(0x01 << 16)	/* Disable Read-Ahead */
 
 #define isascii(c)	(((c) & ~0x7F) == 0)
 
Index: head/sys/boot/common/bcache.c
===================================================================
--- head/sys/boot/common/bcache.c
+++ head/sys/boot/common/bcache.c
@@ -295,7 +295,11 @@
      * Our choice of 16 read ahead blocks will always fit inside the bcache.
      */
 
-    ra = bc->bcache_nblks - BHASH(bc, p_blk + p_size);
+    if ((rw & F_NORA) == F_NORA)
+	ra = 0;
+    else
+	ra = bc->bcache_nblks - BHASH(bc, p_blk + p_size);
+
     if (ra != 0 && ra != bc->bcache_nblks) { /* do we have RA space? */
 	ra = MIN(bc->ra, ra - 1);
 	ra = rounddown(ra, 16);		/* multiple of 16 blocks */
@@ -316,6 +320,7 @@
      * in either case we should return the data in bcache and only
      * return error if there is no data.
      */
+    rw &= F_MASK;
     result = dd->dv_strategy(dd->dv_devdata, rw, p_blk,
 	p_size * bcache_blksize, p_buf, &r_size);
 
@@ -381,10 +386,11 @@
 	((size * 2 / bcache_blksize) > bcache_nblks)) {
 	DEBUG("bypass %zu from %qu", size / bcache_blksize, blk);
 	bcache_bypasses++;
+	rw &= F_MASK;
 	return (dd->dv_strategy(dd->dv_devdata, rw, blk, size, buf, rsize));
     }
 
-    switch (rw) {
+    switch (rw & F_MASK) {
     case F_READ:
 	nblk = size / bcache_blksize;
 	if (size != 0 && nblk == 0)
@@ -423,7 +429,7 @@
 
 	return (ret);
     case F_WRITE:
-	return write_strategy(devdata, rw, blk, size, buf, rsize);
+	return write_strategy(devdata, F_WRITE, blk, size, buf, rsize);
     }
     return -1;
 }
Index: head/sys/boot/common/disk.c
===================================================================
--- head/sys/boot/common/disk.c
+++ head/sys/boot/common/disk.c
@@ -87,7 +87,12 @@
 
 	dev = (struct disk_devdesc *)d;
 	od = (struct open_disk *)dev->d_opendata;
-	return (dev->d_dev->dv_strategy(dev, F_READ, offset,
+
+	/*
+	 * As the GPT backup partition is located at the end of the disk,
+	 * to avoid reading past disk end, flag bcache not to use RA.
+	 */
+	return (dev->d_dev->dv_strategy(dev, F_READ | F_NORA, offset,
 	    blocks * od->sectorsize, (char *)buf, NULL));
 }