oracle 集群组件概念

http://docs.oracle.com/cd/E11882_01/rac.112/e41959/intro.htm#CWADD92367

一、Oracle Clusterware Software Concepts and Requirements

Oracle Clusterware uses voting disk files to provide fencing and cluster node membership determination. OCR provides cluster configuration information. You can place the Oracle Clusterware files on either Oracle ASM or on shared common disk storage. If you
configure Oracle Clusterware on storage that does not provide file redundancy, then Oracle recommends that you configure multiple locations for OCR and voting disks. The voting disks and OCR are described as follows:

Voting Disks

Oracle Clusterware uses voting disk files to determine which nodes are members of a cluster. You can configure voting disks on Oracle ASM, or you can configure voting disks on shared storage.
If you configure voting disks on Oracle ASM, then you do not need to manually configure the voting disks. Depending on the redundancy of your disk group, an appropriate number of voting disks are created.
If you do not configure voting disks on Oracle ASM, then for high availability, Oracle recommends that you have a minimum of three voting disks on physically separate storage. This avoids having a single point of failure. If you configure
a single voting disk, then you must use external mirroring to provide redundancy.
You should have at least three voting disks, unless you have a storage device, such as a disk array that provides external redundancy. Oracle recommends that you do not use more than five voting disks. The maximum number of voting
disks that is supported is 15.

OCR- Oracle Cluster Register

集群注册文件，记录每个节点的相关信息，保存RAC集群的各种资源信息, 存储于共享磁盘上，所有实例共享 默认有2个互备磁盘

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:

You can have up to five OCR locations

Each OCR location must reside on shared storage that is accessible by all of the nodes in the cluster

You can replace a failed OCR location online if it is not the only OCR location

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 Database Configuration
Assistant (DBCA)

Voting Disk 表决磁盘

仲裁机制用于仲裁多个节点向共享节点财时写的行为，避免发生冲突 存储于共享磁盘上，所有实例共享 用于确定各个实例的关系

当有节点失效时，通过voting disk来决定驱逐哪个实例 默认有3个互备磁盘

二、Overview of Oracle Clusterware Platform-Specific Software Components

When Oracle Clusterware is operational, several platform-specific processes or services run on each node in the cluster. This section describes these various processes and services.

The Oracle Clusterware Stack

Oracle Clusterware consists of two separate stacks: an upper stack anchored by the Cluster Ready Services (CRS) daemon (

crsd

) and a lower stack anchored by the Oracle High Availability Services daemon (

ohasd

).
These two stacks have several processes ,that facilitate cluster operations. The following sections describe these stacks in more detail:

The Cluster Ready Services Stack

The Oracle High Availability Services
Stack

oracle 集群组要可以分为两个部分：（1）集群服务（2）高可用性

The Cluster Ready Services Stack

The list in this section describes the processes that comprise CRS. The list includes components that are processes on Linux and UNIX operating systems, or services on Windows.

Cluster Ready Services (CRS): The primary program for managing high availability operations in a cluster.
The CRS daemon

(crsd

) manages cluster resources based on the configuration information that is stored in OCR for each resource. This includes start, stop, monitor, and failover operations. The

crsd

process
generates events when the status of a resource changes. When you have Oracle RAC installed, the

crsd

process monitors the Oracle database instance, listener, and so on, and automatically restarts these components when a
failure occurs.

CRS-集群资源服务(cluster ready services) 管理集群内高可用操作的基本程序 ，CRS管理的任何事务被称之为资源，包括 数据库、实例、监听、虚拟IP、应用进程等等
CRS是跟据存储于OCR中的资源配置信息来管理这些资源 ，当一资源的状态改变时，CRS进程生成一个事件

Cluster Synchronization Services (CSS): 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. If you are using certified third-party clusterware, then CSS processes interface with your clusterware to manage node membership information.
The

cssdagent

process monitors the cluster and provides I/O fencing. This service formerly was provided by Oracle Process Monitor Daemon (

oprocd

), also known as

OraFenceService

on
Windows. A

cssdagent

failure may result in Oracle Clusterware restarting the node.

CSS-集群同步服务(Cluster
Synchronization Service)管理集群节点的成员资格控制哪个结点为集群的成员、节点在加入或离开集群时通知集群成员来控制集群配置信息 此进程发生故障导致集群重启

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

Cluster Time Synchronization Service (CTSS): Provides time management in a cluster for Oracle Clusterware.

CTSS 集群时间同步服务 Cluster Time Synchronization
Service (CTSS)，提供集群时间同步

Event Management (EVM): A background process that publishes events that Oracle Clusterware creates.

EVMD事件管理服务(Event Management) 事件管理守护进程 发布CRS创建事件的后台进程

Oracle Notification Service (ONS): A publish and subscribe service for communicating Fast Application Notification (FAN) events.

ONS-事件的发布及订阅服务(Oracle Notification Service) 通信的快速应用通知事件的发布及订阅服务

Oracle Agent (oraagent): Extends clusterware to support Oracle-specific requirements and complex resources. This process runs server callout scripts when FAN events occur. This process
was known as RACG in Oracle Clusterware 11g release 1 (11.1).

Oracle Root Agent (orarootagent): A specialized

oraagent

process that helps

crsd

manage resources owned by

root

,
such as the network, and the Grid virtual IP address.

The Cluster Synchronization Service (CSS), Event Management (EVM), and Oracle Notification Services (ONS) components communicate with other cluster component layers on other nodes in the same cluster database environment. These components are also the main
communication links between Oracle Database, applications, and the Oracle Clusterware high availability components. In addition, these background processes monitor and manage database operations.

The Oracle High Availability Services Stack

This section describes the processes that comprise the Oracle High Availability Services stack. The list includes components that are processes on Linux and UNIX operating systems, or services on Windows.

Cluster Logger Service (

ologgerd

):
Receives information from all the nodes in the cluster and persists in a CHM repository-based database. This service runs on only two nodes in a cluster.

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.

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.

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

Multicast Domain Name Service (mDNS): Used by Grid Plug and Play to locate profiles in the cluster, as well as by GNS to perform name resolution. The mDNS process is a background process
on Linux and UNIX and on Windows.

Oracle Grid Naming Service (GNS): Handles requests sent by external DNS servers, performing name resolution for names defined by the cluster.