If you need to know it’s been persisted to non-volatile storage then you need to own the full stack of every piece of software between the OS and the actual physical memory.
Every managed flash drive is going to have layers and layers of complexity and caching and things you simply can’t easily control or really understand. Don’t trust it unless you know exactly how it works all the way down.
Famously not, as the man page says.
It is also said later in the article:
> POSIX strictly requires a parent-directory fsync to make a newly created file’s existence durable.
So I'm not sure why the dirent sync is claimed earlier.
EDIT: sketchy from an answering "what exactly are the guarantees?" perspective
I also do have an optional WAL. Maybe I should add an additional mode that disables fsync only for the WAL. I don't think it would be a good idea. My WAL does use checksums and sequence numbers etc. to prevent committing wrong data.
Would you be so kind to explain what happens in a power-loss scenario?