Oracle 12c RAC

Oracle 12c RAC

Oracle RAC 12c introduces two new concepts

Hub Nodes: They are connected among them via private network and have direct access to the shared storage just like previous versions. These nodes are the ones that access the Oracle Cluster Registry (OCR) and Voiting Disk (VD) directly.

Leaf Nodes: These nodes are lighter and are not connected among them, neither access the shared storage like the Hub Nodes. Each Leaf Node communicates with the Hub Node that is attached to, and its connected to the cluster via the Hub Node that is linked to.

Oracle FLEX ASM

In earlier releases (11g), ASM and database instances are tightly coupled with 1:1 mapping. If any ASM instance goes down then corresponding database node also crashes.

Oracle FLEX ASM - Introduced in 12c, ASM and database instances are loosely coupled, means every database node doesn't require ASM instance running on each node to serve storage. In 12c, by default you will get three ASM instances in cluster to server storage. In 12c, ASM instances use dedicated interconnect like database private interconnect in RAC.