1 Introduction to Oracle Clusterware

What is Oracle Clusterware?

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. These resources are generally named ora.entity_name.resource_type_abbreviation, such as ora.mydb.db, which is the name of a resource that is a database. (Some examples of abbreviation are db for database, lsnr for listener, and vip for VIP.) Oracle does not support editing these resources except under the explicit direction of My Oracle Support.

Figure 1-1 shows a configuration that uses Oracle Clusterware to extend the basic single-instance Oracle Database architecture. In Figure 1-1, the cluster is running Oracle Database and is actively servicing applications and users. Using Oracle Clusterware, you can use the same high availability mechanisms to make your Oracle database and your custom applications highly available.

Figure 1-1 Oracle Clusterware Configuration

Description of "Figure 1-1 Oracle Clusterware Configuration"

The benefits of using a cluster include:

• Scalability of applications

• Reduce total cost of ownership for the infrastructure by providing a scalable system with low-cost commodity hardware

• Ability to fail over

• Increase throughput on demand for cluster-aware applications, by adding servers to a cluster to increase cluster resources

• Increase throughput for cluster-aware applications by enabling the applications to run on all of the nodes in a cluster

• Ability to program the startup of applications in a planned order that ensures dependent processes are started in the correct sequence

• Ability to monitor processes and restart them if they stop

• Eliminate unplanned downtime due to hardware or software malfunctions

• Reduce or eliminate planned downtime for software maintenance

You can program Oracle Clusterware to manage the availability of user applications and Oracle databases. In an Oracle RAC environment, Oracle Clusterware manages all of the resources automatically. All of the applications and processes that Oracle Clusterware manages are either cluster resources or local resources.

Oracle Clusterware is required for using Oracle RAC; it is the only clusterware that you need for platforms on which Oracle RAC operates. Although Oracle RAC continues to support many third-party clusterware products on specific platforms, you must also install and use Oracle Clusterware. Note that the servers on which you want to install and run Oracle Clusterware must use the same operating system.

Using Oracle Clusterware eliminates the need for proprietary vendor clusterware and provides the benefit of using only Oracle software. Oracle provides an entire software solution, including everything from disk management with Oracle Automatic Storage Management (Oracle ASM) to data management with Oracle Database and Oracle RAC. In addition, Oracle Database features, such as Oracle Services, provide advanced functionality when used with the underlying Oracle Clusterware high availability framework.

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

Understanding System Requirements for Oracle Clusterware

To use Oracle Clusterware, you must understand the hardware and software concepts and requirements as described in the following sections:

• Oracle Clusterware Hardware Concepts and Requirements

• Oracle Clusterware Operating System Concepts and Requirements

• Oracle Clusterware Software Concepts and Requirements

• Oracle Clusterware Network Configuration Concepts

• Overview of Upgrading and Patching Oracle Clusterware

http://www.oracle.com/technetwork/database/clustering/tech-generic-unix-new-166583.html

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 Technology Stack

Oracle Clusterware consists of two separate technology stacks: an upper technology stack anchored by the Cluster Ready Services (CRS) daemon (CRSD) and a lower technology stack anchored by the Oracle High Availability Services daemon (OHASD). These two technology stacks have several processes that facilitate cluster operations. The following sections describe these technology stacks in more detail:

• The Cluster Ready Services Technology Stack

• The Oracle High Availability Services Technology Stack

The Cluster Ready Services Technology Stack

The following list describes the processes that comprise CRS:

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

  The 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.

• 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.

• 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.

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

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

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

• Oracle Root Agent(orarootagent): A specialized oraagent process that helps the 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 Technology Stack

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

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

  See Also:

  "Resources" for more information about appagent

• 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.

  Note:

  This process is distinctly different from the process of the same name that runs in the Cluster Ready Services technology stack.

• Oracle Root Agent (orarootagent): A specialized oraagent process that helps the CRSD manage resources owned by root, such as the Cluster Health Monitor (CHM).

  Note:

  This process is distinctly different from the process of the same name that runs in the Cluster Ready Services technology stack.

  See Also:

  "Overview of Managing Oracle Clusterware Environments" for more information about CHM

• scriptagent: Protects resources of resource types other than application when using shell or batch scripts to protect an application.

  See Also:

  "Resources" for more information about scriptagent

• 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.

Table 1-1 lists the processes and services associated with Oracle Clusterware components. In Table 1-1, if a UNIX or a Linux system process has an (r) beside it, then the process runs as the root user.

Table 1-1 List of Processes and Services Associated with Oracle Clusterware Components^Foot 1 

Oracle Clusterware Component	Linux/UNIX Process	Windows Processes
Oracle ASMFoot 2
CRS	crsd.bin (r)	crsd.exe
CSS	ocssd.bin, cssdmonitor, cssdagent	cssdagent.exe, cssdmonitor.exe ocssd.exe
CTSS	octssd.bin (r)	octssd.exe
EVM	evmd.bin, evmlogger.bin	evmd.exe
GIPC	gipcd.bin
GNS	gnsd (r)	gnsd.exe
Grid Plug and Play	gpnpd.bin	gpnpd.exe
LOGGER	ologgerd.bin (r)	ologgerd.exe
Master Diskmon	diskmon.bin
mDNS	mdnsd.bin	mDNSResponder.exe
Oracle agent	oraagent.bin (Oracle Clusterware 12c release 1 (12.1) and 11g release 2 (11.2)), or racgmain and racgimon (Oracle Clusterware 11g release 1 (11.1))	oraagent.exe
Oracle High Availability Services	ohasd.bin (r)	ohasd.exe
ONS	ons	ons.exe
Oracle root agent	orarootagent (r)	orarootagent.exe
SYSMON	osysmond.bin (r)	osysmond.exe

^Footnote 1 The only Windows services associated with the Oracle Grid Infrastructure are OracleOHService (OHASD), Oracle ASM, listener services (including node listeners and SCAN listeners), and management database. Oracle ASM can be considered part of the Oracle Clusterware technology stack when OCR is stored on Oracle ASM. The listeners and management database are Oracle Clusterware resources and are not properly part of the Oracle Clusterware technology stack.

^Footnote 2 Oracle ASM is not just one process, but an instance. Given Oracle Flex ASM, Oracle ASM does not necessarily run on every cluster node but only some of them.

See Also:

"Oracle Clusterware Diagnostic and Alert Log Data" for information about the location of log files created for processes

Note:

Oracle Clusterware on Linux platforms can have multiple threads that appear as separate processes with unique process identifiers.

Figure 1-2 illustrates cluster startup.

Figure 1-2 Cluster Startup

Description of "Figure 1-2 Cluster Startup"

Overview of Installing Oracle Clusterware

The following section introduces the installation processes for Oracle Clusterware.

Overview of Upgrading and Patching Oracle Clusterware

Oracle supports out-of-place upgrades, only, because Oracle Clusterware 12c must have its own, new Grid home. For Oracle Clusterware 12c, Oracle supports in-place or out-of-place patching. Oracle supports patch bundles and one-off patches for in-place patching but only supports patch sets and major point releases for out-of-place upgrades.

In-place patching replaces the Oracle Clusterware software with the newer version in the same Grid home. Out-of-place upgrade has both versions of the same software present on the nodes at the same time, in different Grid homes, but only one version is active.

Rolling upgrades avoid downtime and ensure continuous availability of Oracle Clusterware while the software is upgraded to the new version. When you upgrade to Oracle Clusterware 12c, Oracle Clusterware and Oracle ASM binaries are installed as a single binary called the Oracle Grid Infrastructure. You can upgrade Oracle Clusterware in a rolling manner from Oracle Clusterware 10g and Oracle Clusterware 11g, however you can only upgrade Oracle ASM in a rolling manner from Oracle Database 11g release 1 (11.1).

Oracle supports force upgrades in cases where some nodes of the cluster are down.

Overview of Managing Oracle Clusterware Environments

The following list describes the tools and utilities for managing your Oracle Clusterware environment:

• Cluster Health Monitor (CHM): Cluster Health Monitor detects and analyzes operating system and cluster resource-related degradation and failures to provide more details to users for many Oracle Clusterware and Oracle RAC issues, such as node eviction. The tool continuously tracks the operating system resource consumption at the node, process, and device levels. It collects and analyzes the clusterwide data. In real-time mode, when thresholds are met, the tool shows an alert to the user. For root-cause analysis, historical data can be replayed to understand what was happening at the time of failure.

  See Also:

  "Cluster Health Monitor" for more information about CHM

• Cluster Verification Utility (CVU): CVU is a command-line utility that you use to verify a range of cluster and Oracle RAC specific components. Use CVU to verify shared storage devices, networking configurations, system requirements, and Oracle Clusterware, and operating system groups and users.

  Install and use CVU for both preinstallation and postinstallation checks of your cluster environment. CVU is especially useful during preinstallation and during installation of Oracle Clusterware and Oracle RAC components to ensure that your configuration meets the minimum installation requirements. Also use CVU to verify your configuration after completing administrative tasks, such as node additions and node deletions.

  See Also:

  Your platform-specific Oracle Clusterware and Oracle RAC installation guide for information about how to manually install CVU, and Appendix A, "Cluster Verification Utility Reference" for more information about using CVU

• Oracle Cluster Registry Configuration Tool (OCRCONFIG): OCRCONFIG is a command-line tool for OCR administration. You can also use the OCRCHECK and OCRDUMP utilities to troubleshoot configuration problems that affect OCR.

  See Also:

  Chapter 2, "Administering Oracle Clusterware" for more information about managing OCR

• Oracle Clusterware Control (CRSCTL): CRSCTL is a command-line tool that you can use to manage Oracle Clusterware. Use CRSCTL for general clusterware management, management of individual resources, configuration policies, and server pools for non-database applications.

  Oracle Clusterware 12c introduces cluster-aware commands with which you can perform operations from any node in the cluster on another node in the cluster, or on all nodes in the cluster, depending on the operation.

  You can use crsctl commands to monitor cluster resources (crsctl status resource) and to monitor and manage servers and server pools other than server pools that have names prefixed with ora.*, such as crsctl status server, crsctl status serverpool, crsctl modify serverpool, and crsctl relocate server. You can also manage Oracle High Availability Services on the entire cluster (crsctl start | stop | enable | disable | config crs), using the optional node-specific arguments -n or -all. You also can use CRSCTL to manage Oracle Clusterware on individual nodes (crsctl start | stop | enable | disable | config crs).

  See Also:

  • Chapter 2, "Administering Oracle Clusterware" for more information about using crsctl commands to manage Oracle Clusterware

  • Appendix E, "Oracle Clusterware Control (CRSCTL) Utility Reference" for a complete list of CRSCTL commands

• Oracle Enterprise Manager: Oracle Enterprise Manager has both the Cloud Control and Grid Control GUI interfaces for managing both single instance and Oracle RAC database environments. It also has GUI interfaces to manage Oracle Clusterware and all components configured in the Oracle Grid Infrastructure installation. Oracle recommends that you use Oracle Enterprise Manager to perform administrative tasks.

  See Also:

  Oracle Database 2 Day + Real Application Clusters Guide, Oracle Real Application Clusters Administration and Deployment Guide, and Oracle Enterprise Manager online documentation for more information about administering Oracle Clusterware with Oracle Enterprise Manager

• Oracle Interface Configuration Tool (OIFCFG): OIFCFG is a command-line tool for both single-instance Oracle databases and Oracle RAC environments. Use OIFCFG to allocate and deallocate network interfaces to components. You can also use OIFCFG to direct components to use specific network interfaces and to retrieve component configuration information.

  See Also:

  Appendix D, "Oracle Interface Configuration Tool (OIFCFG) Command Reference"

• Server Control (SRVCTL): SRVCTL is a command-line interface that you can use to manage Oracle resources, such as databases, services, or listeners in the cluster.

  Note:

  You can only use SRVCTL to manage server pools that have names prefixed with ora.*.

  See Also:

  Oracle Real Application Clusters Administration and Deployment Guide for more information about SRVCTL

Overview of Cloning and Extending Oracle Clusterware in Grid Environments

Cloning nodes is the preferred method of creating new clusters. The cloning process copies Oracle Clusterware software images to other nodes that have similar hardware and software. Use cloning to quickly create several clusters of the same configuration. Before using cloning, you must install an Oracle Clusterware home successfully on at least one node using the instructions in your platform-specific Oracle Clusterware installation guide.

For new installations, or if you must install on only one cluster, Oracle recommends that you use the automated and interactive installation methods, such as Oracle Universal Installer or the Provisioning Pack feature of Oracle Enterprise Manager. These methods perform installation checks to ensure a successful installation. To add or delete Oracle Clusterware from nodes in the cluster, use the addnode.sh and rootcrs.pl scripts.

Overview of the Oracle Clusterware High Availability Framework and APIs

Oracle Clusterware provides many high availability application programming interfaces called CLSCRS APIs that you use to enable Oracle Clusterware to manage applications or processes that run in a cluster. The CLSCRS APIs enable you to provide high availability for all of your applications.

You can define a VIP address for an application to enable users to access the application independently of the node in the cluster on which the application is running. This is referred to as the application VIP. You can define multiple application VIPs, with generally one application VIP defined for each application running. The application VIP is related to the application by making it dependent on the application resource defined by Oracle Clusterware.

To maintain high availability, Oracle Clusterware components can respond to status changes to restart applications and processes according to defined high availability rules. You can use the Oracle Clusterware high availability framework by registering your applications with Oracle Clusterware and configuring the clusterware to start, stop, or relocate your application processes. That is, you can make custom applications highly available by using Oracle Clusterware to create profiles that monitor, relocate, and restart your applications.

Overview of Cluster Time Management

The Cluster Time Synchronization Service (CTSS) is installed as part of Oracle Clusterware and runs in observer mode if it detects a time synchronization service or a time synchronization service configuration, valid or broken, on the system. For example, if the etc/ntp.conf file exists on any node in the cluster, then CTSS runs in observer mode even if no time synchronization software is running.

If CTSS detects that there is no time synchronization service or time synchronization service configuration on any node in the cluster, then CTSS goes into active mode and takes over time management for the cluster.

If CTSS is running in active mode while another, non-NTP, time synchronization software is running, then you can change CTSS to run in observer mode by creating a file called etc/ntp.conf. CTSS puts an entry in the alert log about the change to observer mode.

When nodes join the cluster, if CTSS is in active mode, then it compares the time on those nodes to a reference clock located on one node in the cluster. If there is a discrepancy between the two times and the discrepancy is within a certain stepping limit, then CTSS performs step time synchronization, which is to step the time, forward or backward, of the nodes joining the cluster to synchronize them with the reference.

Clocks on nodes in the cluster become desynchronized with the reference clock (a time CTSS uses as a basis and is on the first node started in the cluster) periodically for various reasons. When this happens, CTSS performs slew time synchronization, which is to speed up or slow down the system time on the nodes until they are synchronized with the reference system time. In this time synchronization method, CTSS does not adjust time backward, which guarantees monotonic increase of the system time.

When Oracle Clusterware starts, if CTSS is running in active mode and the time discrepancy is outside the stepping limit (the limit is 24 hours), then CTSS generates an alert in the alert log, exits, and Oracle Clusterware startup fails. You must manually adjust the time of the nodes joining the cluster to synchronize with the cluster, after which Oracle Clusterware can start and CTSS can manage the time for the nodes.

When performing slew time synchronization, CTSS never runs time backward to synchronize with the reference clock. CTSS periodically writes alerts to the alert log containing information about how often it adjusts time on nodes to keep them synchronized with the reference clock.

CTSS writes entries to the Oracle Clusterware alert log and syslog when it:

• Detects a time change

• Detects significant time difference from the reference node

• The mode switches from observer to active or vice versa

Having CTSS running to synchronize time in a cluster facilitates troubleshooting Oracle Clusterware problems, because you will not have to factor in a time offset for a sequence of events on different nodes.

To activate CTSS in your cluster, you must stop and deconfigure the vendor time synchronization service on all nodes in the cluster. CTSS detects when this happens and assumes time management for the cluster.

For example, to deconfigure NTP, you must remove or rename the etc/ntp.conf file.

Similarly, to deactivate CTSS in your cluster:

1. Configure the vendor time synchronization service on all nodes in the cluster. CTSS detects this change and reverts back to observer mode.

2. Use the crsctl check ctss command to ensure that CTSS is operating in observer mode.

3. Start the vendor time synchronization service on all nodes in the cluster.

4. Use the cluvfy comp clocksync -n all command to verify that the vendor time synchronization service is operating.