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Oracle Clusterware includes the following processes:                                           Link to Oracle RAC clusterware startup sequence (11gR2)

1) Cluster Ready Services (CRS) 

          Functionality: RAC resource monitoring/ management   ==> all changes are written in the OCR

                                                  - start, stop of the resouces

                                                  - failover of the application resources

                                                  - node recovery

                                                  - automatically restarts t RAC resources when a failure occurs.

          RAC resources: a database, an instance, a service, a listener, a virtual IP (VIP) address, an application process

          Daemon process (on AIX, UNIX, Linux):  crsd

          Run as (on AIX, UNIX, Linux): root

          ps -ef | grep crsd
        root 221524 1 0 May 26 - 3:33 /oracle/crs/10.2/bin/crsd.bin reboot
 

          Failure of the process: the crsd restarts automatically, without restarting the node.

  CRSd can run in 2 modes:

     reboot mode -> when crsd starts all the resources are restarted.

     restart mode -> when crsd starts the resources are started as these were before the shutdown.

   When CRS is installed on the cluster where a 3rd-party clusterware is integrated (there are 2 clusterware on the cluster)

                 -> CRSd manages:

                              -  Oracle RAC services and resources

   When CRS is the ONLY ONE clusterware on the cluster

                 -> CRSd manages:

                              -  Oracle RAC services and resources

                              -  the node membership functionality  (by CSSd, but CSS in managed by CRSd)

   COMMENT:

   In order to start the crsd we need:

                 - the public interface, the private interface and the virtual IP (VIP) should be up and running !

                 - these IPs must be pingable to each other.

2) Cluster Synchronization Services (CSS)

          Functionality: enables basic cluster services    ==> new/ lost node information is written to OCR

                                   - the node membership functionality

                                   - basic locking

          Daemon process (on AIX, UNIX, Linux):  ocssd

          Run as (on AIX, UNIX, Linux): oracle

        ps -ef | grep ocssd
        oracle 229642 241940 1 May 26 - 3:36 /oracle/crs/10.2/bin/ocssd.bin
 

          Failure of the process: Node restart.

3) Event Management (EVM)

          Functionality: - a background process that publishes events that crs creates.

          Daemon process (on AIX, UNIX, Linux):  evmd

          Run as (on AIX, UNIX, Linux): oracle

        ps -ef | grep evmd
        oracle 229633 241356 1 May 26 - 3:36 /oracle/crs/10.2/bin/evmd.bin
 

          Failure of the process: the evmd restarts automatically, without restarting the node.

4) Oracle Notification Service (ONS)

          Functionality: - a publish and subscribe service for communicating Fast Application Notification (FAN) events to clients.

          Daemon process (on AIX, UNIX, Linux):  ons

          Run as (on AIX, UNIX, Linux): oracle

        ps -ef | grep ons
        oracle 233968 1 0 May 28 - 0:00 /oracle/crs/10.2/opmn/bin/ons -d
 

          Failure of the process:  -

5) RACG

6) Process Monitor Daemon (OPROCD)    (cssdagent from 11gR2)

More information about  this subject ( Oracle RAC Clusterware components ) you can get from  www.in-oracle.com