How RDBMS communicates with ASM

- When the ASM instance starts, it registers with the Cluster Synchronization Services (CSS) daemon running as the "bin" user.

- When the RDBMS accesses an ASM file for the first time, it must establish a connection to the local ASM instance.

- No connection details are stored, so no configuration is needed.

- The RDBMS contacts the CSS daemon, which provides the ASM instance connection string.

- The RDBMS then connects to the ASM instance as SYSDBA using OS authentication.

- The initial connection between the RDBMS and ASM instance is called the "umbilicus."

- The umbilicus stays active as long as the RDBMS has any open ASM files.

- The RDBMS ASMB process connects to the ASM instance and remains connected as long as there are open ASM files.

- The ASM side of the connection is handled by a foreground process called the "umbilicus foreground" (UFG).

- Critical messages are exchanged between RDBMS and ASM instances through the umbilicus.

- If the umbilicus fails, the RDBMS instance will experience a fatal issue, as it is critical for maintaining disk group integrity.

Simple Interview Answer can be :

The RDBMS communicates with ASM using OS authentication.

During the first connection, ASM provides a disk extent map to the RDBMS instance, which then reads the data.