There are several steps involved on conversion of a Single Instance Database to RAC, starting from the configuration of the RAC environment, that is
- Install CRS on all nodes
- Install ASM Home on all nodes
- Prepare Shared Storage
That database was built as a clone of a production RAC database. This fact made necessary to do some cleanup before running the conversion.
These cleanup operations are also useful in case you have errors during the convert, and you need to retry it; they are described in the document.
If you prefer to have full control, a very good description of user managed convert is found in OTN: Convert a Single Instance Database to Oracle RAC 10g on RHEL3