It uses SQLite. Which has multiple advantages like speed and reduced risk of interruption over Postgres (as that would be a separate service that could crash and to which the connection could be lost). The data does get backed up once a day.
Each instance has a reserved amount of RAM which depends on the plan that got selected.
It all runs on Azure on servers in Frankfurt. Honestly not idea about the RAID setup Azure uses but all our instances use SSD drives to offer optimal performance.
Speed wise is SQLite top. Is generally already fast but additionally also saves going over the network as in this case the database is kind of built-in.