From Online Manual
All SMF posts, topics, members, settings, calendar entries, etc. are stored on the database. Backup the database frequently in case it is damaged. See Requirements and recommendations for more about the type of database you need Forums using SMF 2.0 and up can use MySQL, PostgreSQL, or SQLite database to store all of the data on the forum, while SMF 1.0 and 1.1 forums may use only MySQL.