diff --git a/tools/test/stress2/misc/fsck8.sh b/tools/test/stress2/misc/fsck8.sh
new file mode 100755
index 000000000000..7b2e20bb7d5b
--- /dev/null
+++ b/tools/test/stress2/misc/fsck8.sh
@@ -0,0 +1,178 @@
+#!/bin/sh
+
+#
+# SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+#
+# Copyright (c) 2022 Peter Holm <pho@FreeBSD.org>
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+# ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+# SUCH DAMAGE.
+#
+
+# fsck_ffs(8) disk image fuzz test. SB focus.
+
+# panic: wrong length 4098 for sectorsize 512
+# FreeBSD 14.0-CURRENT #0 main-n255602-51adf913e8815: Fri May 13 07:55:32 CEST 2022
+# pho@mercat1.netperf.freebsd.org:/usr/src/sys/amd64/compile/PHO
+
+. ../default.cfg
+
+[ `id -u ` -ne 0 ] && echo "Must be root!" && exit 1
+
+cc -o /tmp/flip -Wall -Wextra -O2 ../tools/flip.c || exit 1
+
+set -e
+u1=$mdstart
+u2=$((mdstart + 1))
+mp1=${mntpoint}$u1
+mp2=${mntpoint}$u2
+mkdir -p $mp1 $mp2
+log=$mp1/fsck8.sh.log
+diskimage=$mp1/fsck8.sh.diskimage
+backup=/tmp/fsck8.sh.diskimage.`date +%Y%m%dT%H%M%S`.gz
+asbs=0
+cleans=0
+reruns=0
+waccess=0
+
+max=$((10 * 1024 * 1024))
+# UFS1 or UFS2 SU:
+[ `jot -r 1 0 1` -eq 0 ] && newfs_flags='-O 1' || newfs_flags='-O 2 -U'
+
+mount | grep "on $mp1 " | grep -q /dev/md && umount -f $mp1
+[ -c /dev/md$u1 ] && mdconfig -d -u $u1
+mdconfig -a -t swap -s 1g -u $u1
+newfs $newfs_flags -n /dev/md$u1 > /dev/null
+mount /dev/md$u1 $mp1
+
+[ -c /dev/md$u2 ] && mdconfig -d -u $u2
+dd if=/dev/zero of=$diskimage bs=$max count=1 status=none
+mdconfig -a -t vnode -f $diskimage -u $u2
+backups=`newfs -N $newfs_flags md$u2 | grep -A1 "super-block backups" | \
+    tail -1 | sed 's/,//g'`
+newfs $newfs_flags -n md$u2 > /dev/null
+mount /dev/md$u2 $mp2
+[ -d /usr/include/sys ] && cp -r /usr/include/sys $mp2
+umount $mp2
+set +e
+
+chk() {
+	local i
+
+	clean=0
+	rerun=0
+	waccess=0
+	fsck_ffs -fy $1 > $log 2>&1
+	r=$?
+	if grep -qE "Cannot find file system superblock|Superblock check-hash failed" $log; then
+		for b in $backups; do
+			echo "Using alternate SB $b"
+			asbs=$((asbs + 1))
+			fsck_ffs -b $b -fy $1 > $log 2>&1
+			r=$?
+			grep -qE "Cannot find file system superblock|Superblock check-hash failed" $log ||
+			   break
+		done
+		usedasb=1
+	else
+		usedasb=0
+	fi
+	LANG=C egrep -q "[A-Z][A-Z]" $log && clean=0
+	grep -Eq "IS CLEAN|MARKED CLEAN" $log && clean=1
+	# For now regard a "was modified" as a cause for a rerun,
+	# disregarding the "clean" claim.
+	grep -Eq "WAS MODIFIED" $log && rerun=1
+	grep -q RERUN $log && rerun=1
+	grep -q "NO WRITE ACCESS" $log && waccess=1
+	[ $r -ne 0 -a $clean -eq 1 ] && echo "Exit code $r w/ clean == 1"
+}
+
+cd $mp1
+clean=0
+s=0
+start=`date +%s`
+while [ $((`date +%s` - start)) -lt 300 ]; do
+	mount /dev/md$u2 $mp2 || { s=101; break; }
+	ls -lR $mp2 > /dev/null || { s=102; echo "ls failed"; break; }
+	touch $mp2/`jot -rc 8 a z | tr -d '\n'`
+	while mount | grep -q "on $mp2 "; do umount $mp2; done
+	echo * | grep -q core && break
+	sync
+	mdconfig -d -u $u2
+	# SBLOCK = 64k, SBLOCKSIZE = 8k
+	/tmp/flip -n 5 -s $(((64 + 8) * 1024)) $diskimage
+
+	sync
+	if [ `stat -f%z $diskimage` -gt $max ]; then
+		ls -lh $diskimage
+		truncate -s $max $diskimage
+	else
+		gzip < $diskimage > $backup
+	fi
+	fsync $backup
+
+	for i in `jot 5`; do
+		[ $i -gt 2 ] && echo "fsck run #$i"
+		chk $diskimage
+		[ $rerun -eq 1 ] && { reruns=$((reruns + 1)); continue; }
+		[ $clean -eq 1 ] && { cleans=$((cleans + 1)); break; }
+		[ -f fsck_ffs.core ] &&
+		    { cp $diskimage \
+		        /tmp/fsck_ffs.core.diskimage.`date +%Y%m%dT%H%M%S`; break 2; }
+	done
+	[ $clean -ne 1 ] && break
+	mdconfig -a -t vnode -f $diskimage -u $u2
+	[ $r -ne 0 -a $clean -eq 1 ] &&
+	    { echo "CLEAN && non zero exit code"; break; }
+	[ $clean -eq 1 ] && continue
+	[ $usedasb -eq 1 ] && { echo "Alt. SB failed"; s=104; }
+	[ $waccess -eq 1 ] && { echo "No write access"; s=105; }
+	break
+done
+sleep 2	# Wait for /dev to catch up
+[ -c /dev/md$u2 ] && r1=1 || r1=0
+for i in `jot 5`; do
+	mount | grep -q "on $mp2 " || break
+	umount $mp2 && break
+	sleep 2
+done
+mdconfig -d -u $u2 2>/dev/null # XXX when mount fails
+
+echo "$cleans cleans, $reruns reruns, $asbs alternate SBs."
+if [ $clean -ne 1 ]; then
+	echo "FS still not clean. Last fsck_ffs exit code was $r."
+	echo =================
+	cat $log
+	echo =================
+	cp -v $log /tmp
+	[ $s -eq 0 ] && s=106
+fi
+echo * | grep -q core && { ls -l *.core; cp $log /tmp; exit 106; } ||
+    rm -f $backup
+[ $s -eq 101 ] && rm -f $backup	# mount error breakout
+cd /tmp
+for i in `jot 5`; do
+	umount $mp1 && break
+	sleep 2
+done
+mdconfig -d -u $u1
+rm -f /tmp/flip
+exit $s