Installing Oracle Database 10g with ASM on Linux x86

ASM is not a general-purpose filesystem and can be used only for Oracle data files, redo logs, and control files. Files in ASM can be created and named automatically by the database (by use of the Oracle Managed Files feature) or manually by the DBA. Because the files stored in ASM are not accessible to the operating system, the only way to perform backup and recovery operations on databases that use ASM files is through Recovery Manager (RMAN).

ASM is implemented as a separate Oracle instance that must be up if other databases are to be able to access it. On Linux the OCSSD service (installed by default by the Oracle Universal Installer) must be running to allow use of ASM. Memory requirements for ASM are light: only 64 MB for most systems.

The only one comment I would like to add from myself:-
Scripts "dbstart" and "dbshut" are coming along with every Oracle Release
To manage properly startup and shutdown you have to bring up ASM instance the first and to shutdown ASM instance the last.
To achieve this goal replace just one line for each one of scripts mentioned above

Script $ORACLE_HOME/bin/dbstart:

ORATAB=/etc/oratab
.......

# Comment out 
# cat $ORATAB | while read LINE
# and replace with

cat $ORATAB|grep -v "^#"|sort -d | while read LINE

Script $ORACLE_HOME/bin/dbshut:

ORATAB=/etc/oratab
.......

# Comment out
# cat $ORATAB | while read LINE
# and replace with

cat $ORATAB|grep -v "^#"|sort -dr | while read LINE

Full Story