By default, IBM WebSphere Portal v7.0 installs and uses an Apache Derby database. Installing with Apache Derby lets you quickly get WebSphere Portal installed and running in a proof-of-concept environment. Before using the product extensively, you should visit the IBM Information Center for Portal v7.0 to learn the advantages and disadvantages of using Apache Derby and determine how transferring to another database affects the capacity and scalability of a production environment. Please refer to the following link from IBM: https://www-304.ibm.com/support/docview.wss?uid=swg27019558#Databases_C-worksWith
The Apache Derby database that is installed by default is not intended for use in a production environment or for authoring Web content. Derby does not support clustered environments, enabling security in a database-only mode, or vertical cloned environments in which multiple application servers are configured on a single server. Use one of the other supported databases in a production environment or when authoring Web content because they are better able to handle large amounts of data and can be tuned for performance.
When you choose to transfer data to another supported database such as Oracle or SQL Server or IBM DB2 for LUW (Linux, UNIX, Windows) or DB2 for IBM i, perform the database transfer before you use the portal extensively. Large amounts of data in the databases can cause the database transfer to fail if your Java heap size is not large enough. Because information is added to the databases as you use the Portal, perform the database transfer as soon as it is practical to avoid problems in a production environment.
Data can be transferred from a Derby database, but cannot be transferred to a Derby database. If you are transferring from a database other than the default database, you will need to edit the wkplc.properties, wkplc_dbdomain.properties and wkplc_dbtype.properties files to update the source and target database information.
You can install the database server on the same system as WebSphere Portal, or you can install the database server on a different, also referred to as a remote system.
Using a remote database can have performance benefits. When you are deploying a large scale environment, you can dedicate a server specifically to your database. As more users are accessing the portal, the portal application becomes database intensive. Database activity can take up CPU utilization and disk I/O time. You can increase capacity by separating the database from the server that the Portal is running on increases capacity.
If you install the database server on a remote system, you may be required to install database client software on the WebSphere Portal system so the Portal can communicate with the remote database server.
Documentation in this section is taken directly from IBM WebSphere Portal v7.0 Infocenter.