Ashiwini
28 Jun, 2024
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Oracle Clusterware Startup Sequence

Oracle Clusterware is a comprehensive and integrated cluster management solution provided by Oracle Corporation. It is designed to ensure high availability and scalability for Oracle and non-Oracle applications running in a clustered environment. Oracle Clusterware enables the clustering of servers so they can work together as a single system, thus providing redundancy and high availability.

The benefits of using a cluster include:

Fault Tolerance: Provides automatic failover and recovery, ensuring minimal downtime and continuous availability of services and databases.
Improved Performance: Distributes workloads across multiple nodes, improving overall system performance and response times.
Scalability: Easily add or remove nodes to adjust to changing workloads and business requirements without significant downtime or disruption.
Centralized Management: Simplifies the management and monitoring of cluster resources through centralized tools and interfaces.

Below command will display the status of all cluster resources:

$ ./crsctl status resource -t

The following list describes the processes in the Oracle High Availability Services technology stack:

appagent: Protects any resources of the application resource type used in previous versions of Oracle Clusterware.

Cluster Logger Service (ologgerd): Receives information from all the nodes in the cluster and persists in an Oracle Grid Infrastructure Management Repository-based database. This service runs on only two nodes in a cluster.

Grid Interprocess Communication (GIPC): A support daemon that enables Redundant Interconnect Usage.

Grid Plug and Play (GPNPD): Provides access to the Grid Plug and Play profile, and coordinates updates to the profile among the nodes of the cluster to ensure that all of the nodes have the most recent profile.
Multicast Domain Name Service (mDNS): Used by Grid Plug and Play to locate profiles in the cluster, and by GNS to perform name resolution. The mDNS process is a background process on Linux and UNIX and on Windows.
Oracle Agent (oraagent): Extends clusterware to support Oracle-specific requirements and complex resources. This process manages daemons that run as the Oracle Clusterware owner, like the GIPC, GPNPD, and GIPC daemons.
Oracle Root Agent (orarootagent): A specialized oraagent process that helps the CRSD manage resources owned by root, such as the Cluster Health Monitor (CHM).
System Monitor Service (osysmond): The monitoring and operating system metric collection service that sends the data to the cluster logger service. This service runs on every node in a cluster.

The Oracle Clusterware Technology Stack

The following list describes these processes:

1. Oracle Clusterware

Oracle Clusterware is the foundation of the technology stack, providing the essential services and components needed to run Oracle RAC and other clustered applications.

Key Components:

Oracle Cluster Registry (OCR): Stores configuration information for the cluster, including details about cluster nodes, databases, and other resources.
Voting Disk: Used to determine node membership in the cluster and to help avoid split-brain scenarios by ensuring that only one subset of nodes can operate the cluster.

2. Cluster Ready Services (CRS)

CRS manages high availability operations, including node membership, node fencing, and recovery operations within the cluster. It ensures that the cluster nodes are synchronized and operating correctly.

3. Oracle High Availability Services (OHAS)

OHAS monitors and manages the Oracle Clusterware processes. It ensures that all critical services are running and restarts them if they fail.

4. Oracle Cluster Synchronization Services (CSS)

CSS manages the synchronization and coordination of nodes in the cluster to ensure consistent operation. It ensures that all nodes in the cluster are aware of each other and are working together harmoniously.

5. Event Management (EVM)

EVM tracks and responds to cluster events, such as node failures, instance crashes, and resource state changes. It generates alerts and notifications to inform administrators of critical events within the cluster.

6. Automatic Storage Management (ASM)

ASM is an integrated storage management solution that simplifies the management of database storage. It provides efficient file management and ensures optimal performance by evenly distributing data across all available storage resources.

Key Features of ASM:

Striping: Distributes data evenly across all available disks, improving performance.
Mirroring: Provides redundancy by duplicating data across multiple disks.
Dynamic Rebalancing: Automatically rebalances data when disks are added or removed, ensuring optimal performance and availability.

7. Oracle Grid Infrastructure

Oracle Grid Infrastructure is a bundled installation that includes Oracle Clusterware and Automatic Storage Management (ASM). It provides the necessary infrastructure to manage both Oracle RAC databases and standalone databases.

8. Oracle Real Application Clusters (RAC)

Oracle RAC enables multiple instances running on different nodes to access a single database simultaneously, providing high availability, scalability, and fault tolerance.

9. Oracle Universal Installer (OUI)

OUI is the tool used to install Oracle Clusterware and other Oracle software components. It provides a user-friendly interface for installing, configuring, and managing Oracle products.

10. Oracle Cluster Verification Utility (CVU)

CVU is a tool that performs various checks to ensure that the cluster environment is correctly configured and functioning properly. It verifies network connectivity, shared storage, node compatibility, and other critical components.

11. Oracle Enterprise Manager (OEM)

OEM provides a centralized management console for monitoring and managing Oracle Clusterware, Oracle RAC, and other Oracle software components. It offers a comprehensive set of tools for performance monitoring, configuration management, and alerting.

Oracle Cluster Registry

Oracle Clusterware uses the Oracle Cluster Registry (OCR) to store and manage information about the components that Oracle Clusterware controls, such as Oracle RAC databases, listeners, virtual IP addresses (VIPs), and services and any applications. OCR stores configuration information in a series of key-value pairs in a tree structure. To ensure cluster high availability, Oracle recommends that you define multiple OCR locations. In addition:
1 .You can have up to five OCR locations.
2 .Each OCR location must reside on shared storage that is accessible by all of the nodes in the cluster.
3 .You can replace a failed OCR location online if it is not the only OCR location.
4 .You must update OCR through supported utilities such as Oracle Enterprise Manager, the Oracle Clusterware Control Utility (CRSCTL), the Server Control Utility (SRVCTL), the OCR configuration utility (OCRCONFIG), or the Oracle Database Configuration Assistant (Oracle DBCA)

Voting Files

Oracle Clusterware uses voting files to determine which nodes are members of a cluster. You can configure voting files on Oracle ASM, or you can configure voting files on shared storage.
If you configure voting files on Oracle ASM, then you do not need to manually configure the voting files. Depending on the redundancy of your disk group, an appropriate number of voting files are created.
If you do not configure voting files on Oracle ASM, then for high availability, Oracle recommends that you have a minimum of three voting files on physically separate storage. This avoids having a single point of failure. If you configure a single voting file, then you must use external mirroring to provide redundancy.
Oracle recommends that you do not use more than five voting files, even though Oracle supports a maximum number of 15 voting files.