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This topic to understand the hierarchical directory tree of a sample Optimal Flexible Architecture (OFA)-compliant database for Oracle RAC.

Understanding the Oracle RAC Directory Structure

When you install Oracle Database 18c with Oracle RAC, all subdirectories except for the Oracle Inventory directory, the Oracle Automatic Storage Management home (if applicable), and the Oracle Clusterware home, are under a top-level Oracle base directory. The Oracle home and admin directories are also located under the Oracle base directory.

Directory Structure for A Sample OFA-Compliant Environment.

Directory Description
$ORACLE_BASE The default ORACLE_BASE directory, where the software owner is the oracle user. For example:

/u01/app/oracle
installation_type Type of installation under the Oracle base directory. For example, when installing Oracle Database 18c , the value for installation type is product/18.0.0/dbhome_1. For example:

/u01/app/oracle/product/18.0.0/dbhome_1
$ORACLE_HOME The location in which the Oracle Database software is installed. You can also choose to add a counter, if you have multiple installations of the software. For example, if you are creating a second Oracle home for the Oracle Database 18c software, then the path is as follows:

/u01/app/oracle/product/18.0.0/dbhome_2

Note that the Oracle database home is under the Oracle base directory path. An Oracle Clusterware directory must not be under the Oracle base directory path where the database executable files are located.
dbs The directory in which the local initialization parameter file is stored for the database.
admin The administrative directory. Note that with Oracle Database 11g, bdump, cdump, and udump files are relocated to the directory associated with ADR_BASE. For example:

/u01/app/oracle/admin
db_unique_name The database unique name; this is the same as dbname when the database name is 8 or fewer characters in length. For example, if your database name is sales, the directory path is:

/u01/app/oracle/admin/sales
/hdump

/pfile

 The dump destinations for database server.
$ADR_BASE/bdump

$ADR_BASE/cdump

$ADR_BASE/udump

 Automatic Diagnostic Repository dump destination trace files. Note that this directory path is set by the initialization parameter DIAGNOSTIC_DEST, and that the path for the Automatic Data Repository must be located on a shared storage location available to all the nodes.

By default, this path is a subset of the Oracle base directory, in the following path:

$ORACLE_BASE/diag/
Oracle Grid Infrastructure for a cluster home (Grid home) An OFA-compliant path for the Oracle Clusterware home. The default value is:

/u01/app/18.0.0/grid

During the Oracle Grid Infrastructure for a cluster installation, Oracle Clusterware and Oracle Automatic Storage Management (Oracle ASM) software is installed. The root.sh script changes permissions of all of the parent directories of the Oracle Clusterware home directory to grant write access only to the root user. Because of this, the Oracle Clusterware home directory must not be a subdirectory of the Oracle base directory.
bin The subtree for Oracle Clusterware and Oracle ASM executable files.
network The subtree for Oracle Net Services configuration files and utilities.