Comment by vidarh

ReiserFS was built on the premise that doing a filesystem right could get us to a point where the filesystem is the database for a lot of use cases.

It's now "somewhat possible" in that modern filesystem are overall mostly less broken about handling large number of small (or at least moderately small) files than they used to be.

But databases are still far more optimized for handling small pieces of data in the ways we want to handle data we put into databases, which typically also includes a need to index etc.