RAC study notebook --Oracle Clusterware

in oracle1o.2, CRS has been renamed to Oracle Clusterware and is mandatory in Linux RAC environments, since third-party Clusterware si not support by Oracle on the Linux platform.
--多霸道oracle

Oracle Clusterware is installed as part of the RAC installation process.
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In addition, in Oracle 10.2 and above, Oracle Clusterware provides a High Availability Framework that can support third-party applications running in a clustered environment, enabling them to be maintained in a running state at all times.

In a RAC envrionment it is necessary to install and configure Oracle Clusterware before installing the Oracle database software. A separate ORACLE_HOME directory must be created for oracle clusterware. This directory continues to be referred to as CRS_HOME in the Oracle 10.1 CRS terminology.

Oracle Clusterware consists of the following components:
. Cluster synchronization Services(CSS) : manages cluster node membership
--CSS 主要是管理node成员
. Cluster Ready Services(CRS): performs management operations and high availability recovery
--CRS 执行管理操作和HA 恢复
. Event Manager(EVM) manages event notifications and callouts

In Oracle 10.2 , the installation of Oracle Clusterware has been significantly improved, mainly by the inclusion of the Cluster Verification Utility(CLUVFY), which can be used to check that each stage of the process has been successfully completeed.

when Oracle Clusterware is installed , entries are added to the /etc/inittab file, and the init process spawns the EVMD, OCSSD, and CRSD processes when the node is rebooted.
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h1:35:respawn:/etc/init.d/init.evmd run >/dev/null 2>&1 h2:35:respawn:/etc/init.d/init.cssd fatal >/dev/null 2>&1 h3:35:respawn:/etc/init.d/init.crsd run >/dev/null 2>&1 -------------------


Oracle Cluster Registry
In Oracle 10.1 and above, shared storage must also be available for the OCR in which Oracle stores details of the cluster configuration, including the names and current status of the database, associated instances, services, and node applications , such as the listener process. The OCR is used by Oracle Clusterware and is managed by a number of tools, including the database configuration Assistant(DBCA), Enterprise Manager(EM), and the Server Control(SRVCTL) command-line utility.

The OCR can be stored on a raw device or on a cluster file system. It cannot , however, be stored on an automatic Storage Management(ASM) file system.

In Oracle 10.2 and above, the OCR can be mirrored, eliminating the potential for it to become a single point of failure. A maximum of two copies can be maintained by Oracle Clusterware.

Voting Disk:
shared storage is also required for a voting(or quorum) disk, which is used to determine the nodes that are currently available within the cluster. the voting disk is used by the OCSSD to detect when nodes join and leave the cluster and is therefore also known as the cluster synchronization services (CSS) voting disk.

the Voting disk has similar storage characteristics to the OCR, it can be stored on a raw device or on a cluster file system. it cannot be stored on an ASM file system.

In Oracle 10.2 and above ,t he voting disk can be mirrored , eliminating the potential for it to become a single point of failure. By default, three copies of the voting disk will be created.
Oracle recommends that an odd number of voting disk copies is maintained.