Before you can create an Oracle RAC database using DBCA you must configure your system to meet the software requirements, if you did not complete your system configuration during the Oracle Grid Infrastructure installation.

• Load SSH Keys Into Memory Before Starting DBCA
  In an Oracle RAC environment, you must load SSH keys into memory for the terminal session where you start DBCA. If you do not do this, then you receive user equivalency errors when you attempt to start DBCA.
• Decide on a Naming Convention to Use for Your Oracle RAC Database
  Review this information for naming conventions for Oracle RAC database.
• Configure Shared Storage for the Oracle RAC Database
  Before starting DBCA to configure an Oracle RAC database, you must have installed Oracle Grid Infrastructure for a cluster, and you must have configured shared storage areas for Oracle RAC files.