The DIAGNOSTIC_DEST initialization parameter specifies the directory where diagnostics for an instance are located. The default value for an Oracle ASM instance is the $ORACLE_BASE directory for the Oracle Grid Infrastructure installation.
Example 3-1 shows an example of the diagnostic directory for an Oracle ASM instance.
Oracle Database Administrator's Guide for more information about the DIAGNOSTIC_DEST initialization parameter and the fault diagnosability infrastructure.
Oracle Database Reference for more information about the DIAGNOSTIC_DEST parameter