Oracle Clusterware

Oracle Clusterware is the portable [clusterware], which is required to run the real application clusters options. It provides the basic clustering support at the operating system level and enables Oracle software to run in clustering mode. In earlier versions of Oracle (version 9i and below), RAC required a vendor supplied clusterware like Sun Cluster or Veritas Cluster Server with the exception of Linux and Windows.

Oracle Clusterware Components:

Oracle Clusterware is the software, which enables the nodes to communicate each other, and forms the cluster and makes the nodes as single logical server. Oracle Clusterware is run by Cluster Ready Services using two key components. They are [Oracle Cluster Registry] (OCR), which records and maintains the cluster and node membership information. The other component is voting disk, which acts a tiebreaker during communication failures. Consistent heartbeat information from all the nodes is sent to voting disk when the cluster is running. CRS service has four components namely OPROCd, CRS Daemon (crsd), Oracle Cluster Synchronization Service Daemon (OCSSD) and Event Volume Manager Daemon (evmd) and each handles a variety of functions. Failure or death of the CRS daemon can cause the node failure and it automatically reboots the nodes to avoid the data corruption because of the possible communication failure between the nodes. The CRS daemon runs as the super user ‘root’ in the UNIX platforms and runs as a service in the windows platforms.