Besides trace files, the trace subdirectory in the Oracle Clusterware ADR home contains the simple text Oracle Clusterware alert log. It always has the name alert.log. The alert log is also written as an XML file in the alert subdirectory of the ADR home, but the text alert log is most easily read.
The alert log is the first place to look when a problem or issue arises with Oracle Clusterware. Unlike the Oracle Database instance alert log, messages in the Oracle Clusterware alert log are identified, documented, and localized (translated). Oracle Clusterware alert messages are written for most significant events or errors that occur.
Note:
Messages and data written to Oracle Clusterware trace files generally are not documented and translated and are used mainly by My Oracle Support for problem diagnosis.