echo '1' 2>&1 > /sys/fs/xfs/sdb/error/fail_at_unmount
echo '0' 2>&1 > /sys/fs/xfs/sdb/error/metadata/EIO/max_retries
echo '0' 2>&1 > /sys/fs/xfs/sdb/error/metadata/EIO/retry_timeout_seconds
umount: /dev/sdb: not mounted.