ASM Instance Discovery

In this article I thought will give you quick points that help to understand how RDBMS discover ASM.

RDBMS Discovery of ASM

1. ASM Instance registers with Cluster Synchronization Services (CSS) daemon running as bin when it starts.
2. RDBMS when tries to access the ASM file for the first time, it needs to establish connection to the local ASM instance. These connection details are NOT stored anywhere and you don’t need to configure them. RDBMS contact CSS daemon and gets passed the connect string for the ASM Instance. The RDBMS then connects as sysdba to the ASM instance using OS authentication.
3. The initial connection between the ASM instance and the RDBMS instance is known as the umbilicus, and remains active as long as the RDBMS instance has any ASM files open.
4. RDBMS‘s ASMB process that connects to ASM Instance. It will remain connected till there are open ASM files.
5. The ASM side of the connection is a foreground process , called the umbilicus foreground (UFG).
6. RDBMS and ASM instances exchange critical messages over the umbilicus.
7. Failure of the umbilicus is fatal to the RDBMS instance because the connection is critical to maintaining the integrity of the disk group.

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