[tobias3]

On the contrary. Btrfs had a long standing issue where you could make the filesystem checksums not match with non-stable O_DIRECT writes (so even with a single disk).

This has only recently been fixed by disabling O_DIRECT for files with checksums (so the default): https://lore.kernel.org/linux-btrfs/54c7002136a047b7140c3647...

ZFS has O_DIRECT do nothing as well, as far as I know.