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Oracle Clusterware consists of two separate stacks: the Cluster Ready Service (CRS) daemon (crsd) and the Oracle High Availability Service daemon (ohasd).

The list in this section describes the composition of CRS, including processes on Linux and UNIX or service on windows.

CRS: the main program used to manage high availability operations in a cluster. The crs daemon (crsd manages cluster resources based on the configuration information stored in the ocr of each resource. This includes start, stop, monitoring, and failover operations. The crsd resource state change is that the process generates an event. After installing Oracle RAC, the crsd process monitors Oracle instance,listener, and so on. And automatically restart these components in the event of a failure.

CSS: cluster synchronization service that manages the configuration of the cluster by controlling which nodes are members of the cluster and notifying the members when the nodes join or leave the cluster. If you are using certified third-party cluster software, the css process will interface with your cluster software to manage node membership information. This cssdagent process monitors the cluster and provides Ihampar O protection. This service was previously provided by Oracle Process Monitor Daemon (oprocd), and the failure of cssdagent may cause the Oracle cluster to restart the node.

Oracle ASM: provides disk management for Oracle Clusterware and Oracle Database.

CTSS: the cluster time synchronization service provides time management in the cluster for Oracle Clusterware.

EVM: the event management background process that publishes events created by Oracle Clusterware.

ONS:Oracle Notification Service is a publish and subscribe service that delivers notifications for fast applications.

The Oraagent:Oracle agent extends the cluster software to support Oracle-specific requirements and complex resources. When the FAN event occurs, this process runs the server annotation script, which is called RACG in Oracle Clusterware 11.1.

Orarootagent:Oracle Root Agent is a specialized oraagent process that helps crsd manage the root resources it owns, such as cluster synchronization services (css) event management (EVM) and ONS components in network and grid virtual IP sites communicate with other cluster component layers on other node in the same cluster database environment. These components are also the main communication links between Oracle databases, applications, and Oracle Clusterware. In addition, these background processes monitor and manage database operations.

Oracle High availability Service Architecture

This section describes the process that makes up an Oracle High Availability Service.

Ologgerd: the cluster logger service accepts information from all nodes in the cluster and stores it in a database based on the CHM repository, which runs on only two nodes in the cluster.

Osysymond: the system Monitor service sends data to the cluster logger service's monitoring and operating system metrics service. This service runs on each nodes.

GPNPD: provides access to plug and play profiles and coordinates profile updates between cluster nodes to ensure that all nodes have up-to-date profiles.

GIPC: a daemon that enables the use of redundant interconnects.

GNS: handles requests sent by external DNS servers and resolves the names defined by the cluster.

Summary:Fragmented learning may not work for you.The next blog introduces OCR,Voting Disk,Split Brain,heartbeat in RAC.

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