RelStorage is a drop-in replacement for FileStorage or ZEO that uses a relational database like PostgreSQL as the storage backend. It provides faster commits and concurrency compared to FileStorage by optimizing caching and storing blobs in the database. Setup involves adding RelStorage and a database driver like psycopg2 to a Plone buildout configuration and specifying the database connection details. Existing storages can be converted to RelStorage using zodbconvert.