Even with journaling, you might need one. ZeroFS [0] almost had a lost+found directory (even with the WAL enabled), because you might have consistency issues between your in-memory state and what was flushed, and especially in what order.

ZeroFS ended up not needing recovery at all through atomic, strictly ordered commits [1], but it was far from trivial (and not just a matter of requiring a WAL).

[0] https://github.com/Barre/ZeroFS

[1] https://github.com/Barre/ZeroFS/blob/main/zerofs/src/fs/writ...