All you "must be stupid not to use rdbms" people need to pry open your minds a little.

There are all sorts of apps that use mem/fs for storage. Like mail servers, news servers, squid servers, static http servers, log files, and sql servers (discounting direct io)

rdbms are (usually) just another layer ontop of fs. A very usefull layer if you need what they offer. But if not just a layer of complexity and wasted mem/cpu.

Modern fs have journaling and smart buffering/caching. They kind of rock and discounting them out of hand is a mistake.