OpenMeetings default configuration is to use Apache Derby.
It is recommended for production environments and high availibility to change to an usual relational database like MySQL, Postgres or DB2.
For more information about Apache Derby see http://db.apache.org/derby/
There is a sample configuration for Apache Derby that ships with
every release in:
If you encounter issues, you can drop the db again and delete the file /webapps/openmeetings/conf/install.xml and then run the web based installer again