ZFS gets a lot of the way there - and indeed has lots of similarities to a database in its internals. (In fact, ZFS with `sync=always` set on the dataset would

ZFS gets a lot of the way there - and indeed has lots of similarities to a database in its internals. (In fact, ZFS with `sync=always` set on the dataset would do exactly what the parent commenter is asking for without requiring a whole new API. If someone really cared about performance they could even make this perform well with a battery-backed DRAM device for their intent log... but by that point we're way outside of the discussion of a general-purpose filesystem. If you really need guaranteed consistency for every write _without_ crippling performance, ZFS can do it for you at a hardware cost. Writes get cached in RAM, batched, flushed in transaction groups, and the fast/durable SLOG protects against corruption or loss of power or device failure without harming performance much. $$$ though. You'd better have quite a bit of RAM, and need a proper enterprise-grade DRAM storage device - or probably two in a mirror if your data is this critical).