diff --git a/sys/fs/tarfs/tarfs_vnops.c b/sys/fs/tarfs/tarfs_vnops.c
--- a/sys/fs/tarfs/tarfs_vnops.c
+++ b/sys/fs/tarfs/tarfs_vnops.c
@@ -38,11 +38,19 @@
 #include <sys/mount.h>
 #include <sys/namei.h>
 #include <sys/proc.h>
+#include <sys/sysctl.h>
 #include <sys/vnode.h>
 
 #include <fs/tarfs/tarfs.h>
 #include <fs/tarfs/tarfs_dbg.h>
 
+static int bmap_readbehind = 1;
+SYSCTL_INT(_vfs_tarfs, OID_AUTO, bmap_readbehind, CTLFLAG_RWTUN,
+    &bmap_readbehind, 0, "Enable read-behind for block mapping operations");
+static int readahead_max = -1;
+SYSCTL_INT(_vfs_tarfs, OID_AUTO, readahead_max, CTLFLAG_RWTUN,
+    &readahead_max, 0, "Maximum read-ahead in blocks");
+
 static int
 tarfs_open(struct vop_open_args *ap)
 {
@@ -173,9 +181,11 @@
 	}
 
 	rmax = vp->v_mount->mnt_iosize_max / iosize - 1;
+	if (readahead_max >= 0 && rmax > readahead_max)
+		rmax = readahead_max;
 	*ap->a_runp = imin(ra, rmax);
 	if (ap->a_runb != NULL)
-		*ap->a_runb = imin(rb, rmax);
+		*ap->a_runb = bmap_readbehind ? imin(rb, rmax) : 0;
 	return (0);
 }