network heartbeat

Introduction

In RAC, CSSD processes (Cluster Services Synchronization Daemon) monitor the health of RAC nodes employing two distinct heart beats: Network heart beat and Disk heart beat. Healthy nodes will have continuous network and disk heartbeats exchanged between the nodes. Break in heart beat indicates a possible error scenario. There are few different scenarios possible with missing heart beats:

1. Network heart beat is successful, but disk heart beat is missed.
2. Disk heart beat is successful, but network heart beat is missed.
3. Both heart beats failed.

In addition, with numerous nodes, there are other possible scenarios too. Few possible scenarios: