if mdadm -CfR $md0 -l 5 -n3 $dev0 $dev1 $dev2 --write-zeroes ; then
  check nosync
  echo check > /sys/block/md0/md/sync_action;
  check wait
elif grep "zeroing [^ ]* failed: Operation not supported" \
     $targetdir/stderr; then
  echo "write-zeros not supported, skipping"
else
  echo >&2 "ERROR: mdadm return failure without not supported message"
  exit 1
fi