Oracle Database 10g introduced Cluster Ready Services (CRS), which was the logical next step in the evolution of the clusterware provided by Oracle. CRS is provided to cluster together nodes on any supported operating system, whether Linux, Solaris, AIX, Windows or HP/UX, or another system.
It is possible to use CRS instead of the OS vendor clusterware or third-party clusterware on any of these platforms. It is also possible to use CRS alongside third-party or operating system clusterware: if the maximum availability (MA) DBA chooses to stick with the vendor-provided or third-party clusterware, CRS can be used to integrate Oracle clustering with the existing clusterware, allowing the Oracle RDBMS to also communicate and work correctly with the vendor clusterware. This is done by ensuring that the third-party clusterware is installed before installing Oracle clusterware. All combinations of third-party clusterware may not be supported, so it is a good idea to check the certification site at support.oracle.com to confirm. Assuming the combination of third-party clusterware and Oracle clusterware is supported, a file usually called libskgxn.so (extention may be .a on some O/S’s) will be created in the /opt/ORCLcluster/ directory by the third-party clusterware installation either automatically or via manual steps.
It is important to note that Oracle does not support adding third-party clusterware after Oracle Clusterware has been installed. If third-party clusterware is absolutely required, then it requires Oracle clusterware to be re-installed. Any other workaround can cause problems and is not supported by Oracle.
CRS is supported to run Oracle RAC with the Standard Edition of Oracle, although some limitations and requirements apply that are documented in the install guide.