Clusterware1   introduction to oracle clusterware

1. What is oracle clusterware

Oracle Clusterware enables servers to communicate with each other, so that they appear to function as a collective unit. This combination of servers is commonly known as a cluster.

Oracle Clusterware provides the infrastructure necessary to run Oracle Real Application Clusters (Oracle RAC). Oracle Clusterware also manages resources, such as virtual IP (VIP) addresses, databases, listeners, services, and so on.

Oracle Clusterware has two stored components, besides the binaries: The voting disk files, which record node membership information, and the Oracle Cluster Registry (OCR), which records cluster configuration information. Voting disks and OCRs must reside on shared storage available to all cluster member nodes.

2、System Requirements for Oracle Clusterware

2.1、Oracle Clusterware Hardware Concepts and Requirements

（1）second network as the interconnect

A cluster consists of one or more servers. The hardware in a server in a cluster (or cluster member or node) is similar to a standalone server. However, a server that is part of a cluster, otherwise known as a node or a cluster member, requires a second network. This second network is referred to as the interconnect. For this reason, cluster member nodes require at least two network interface cards: one for a public network and one for a private network。

（2）multipath

To provide redundancy for storage, generally provide at least two connections from each server to the cluster-aware storag

2.2 Oracle Clusterware Operating System Concepts and Requirements

When the operating system is installed and working, you can then install Oracle Clusterware to create the cluster. Oracle Clusterware is installed independently of Oracle Database. Once Oracle Clusterware is installed, you can then install Oracle Database or Oracle RAC on any of the nodes in the cluster.

2.3 Oracle Clusterware Software Concepts and Requirements

（1）Voting Disks

Oracle Clusterware uses voting disk files to determine which nodes are members of a cluster。

（2）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

3、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

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).

3.1 The Cluster Ready Services Stack

（1）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.

（2）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

（3）Cluster Time Synchronization Service (CTSS):

Provides time management in a cluster for Oracle Clusterware.

（4）Event Management (EVM):

 A background process that publishes events that Oracle Clusterware creates.

（5）Oracle Notification Service (ONS):

 A publish and subscribe service for communicating Fast Application Notification (FAN) events

（6）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).

（7）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.

（8）Oracle ASM:

Provides disk management for Oracle Clusterware and Oracle Database.

3.2 The Oracle High Availability Services Stack

This section describes the processes that comprise the Oracle High Availability Services stack.

（1）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.

（2）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.

（3）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.

（4）Grid Interprocess Communication (GIPC):

A support daemon that enables Redundant Interconnect Usage.

（5） 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.

（6）Oracle Grid Naming Service (GNS):

 Handles requests sent by external DNS servers, performing name resolution for names defined by the cluster.