Cluster Background process:

Cluster Background process:

There are difference between Rac and Cluster Background process. Cluster background Discription are Below:

A.Cluster ready Service Daemon (CRSD)
B.Cluster Synchronization Service (CSS)
C.Event Management Daemon (EVMD)
D.Disk Monitor daemon (diskmon)
E.Oracle Notification Service (ONS)

A.Cluster ready Service Daemon (CRSD)

1.Oracle clusterware uses CRS for interaction between the OS and the Database.
2.This metadata is stored in the OCR.
3.It is managing high availability operations in a cluster.
4.The crsd process generates events when the status of a resource changes.

B.Cluster Synchronization Service (CSS)

1.Manages the cluster configuration by controlling which nodes are members of the cluster and by notifying members
 when a node joins or leaves the cluster.
2.Oracle Clusterware performs synchronization of group/locks for the node.
3.Prevents data corruption in event of a split brain.
4.Read voting disk to determine the number and names of members in the cluster.
5.CSS tries to establish connection to all nodes in the cluster using the private interconnect.
6.CSS verifies the number of nodes already registered as part of the cluster by performing an active count function.
7.If no MASTER node has been established CSS authorizes the first node that attains the ACTIVE state as MASTER.
8.Read voting disk to determine the number and names of members in the cluster.
9.Determines the location of the OCR from the ocr.loc file and reads the OCR file to determine the location of the voting  disk.
10.CSS performs state changes to bring the voting disk online.

C.Event Management Daemon (EVMD)

1.It is a background process that publishes Oracle Clusterware events.
2.It is propagates events through the Oracle Notification Service (ONS).
3.EVMD is the communication bridge between the Cluster-Ready Service Daemon (CRSD) and CSSD.[ All communications between the
CRS and CSS happen via the EVMD].

D.Disk Monitor daemon (diskmon)

1.Monitors and performs input/output fencing for Oracle Exadata Storage Server.
2.Exadata storage can be added to any Oracle RAC node at any point in time, the diskmon daemon is always started when ocssd is start.

E.Oracle Notification Service (ONS)

1. It keeps the high availability information.
2.Whenever state of cluster resource changes ONS process , each node will communicate with each other .
3.It is a publish-and-subscribe service for communicating Fast Application Notification (FAN) events.