An little overview of RAC Architecture :
Hardware architecture : disk storage (NAS, SAN, I-SCSI), network protocol recommended : UDP over GigE.
File Systems and Volume Managment : ASM, OCFS
The Benefits of RAC : High Availability and scalability (parallel execution across several nodes.
Managment of RAC Database with Enterprise Manager
Workload Managment : service level, priorities, ressource manager, Oracle Net Service and load balancing, FAN (Fast Application Notification : ie the link between the RAC database and the application).