The document said: "To support large files, increase this limit to at least 8MB. This will activate chunk storage in MySQL."

I set it to 5mb, and config local file storage engine.
But when trying upload a file(24mb), it still stored in MySQL.

Chunk size set in PhabricatorChunkedFileStorageEngine.php maybe the reason.
Limit bigger then 4*1024*1024 will be used as chunked engine.

Step:

1. set mysql-engine.max-size to 5mb
2. set local file storage path
3. upload file about 24mb by drop and drup
4. check where the file stored