DISCLAIMER : Not an Oracle DBA
Use srvctl, the grid control program that allows you to manipulate parts of the RAC Cluster
Usage: srvctl <command> <object> [<options>]
commands: enable|disable|start|stop|relocate|status|add|remove|modify|getenv|setenv|unsetenv|config
objects: database|instance|service|nodeapps|vip|asm|diskgroup|listener|srvpool|server|scan|scan_listener|oc4j|home|filesystem|gns
For detailed help on each command and object and its options use:
srvctl <command> -h or
srvctl <command> <object> -h
Examples
srvctl stop database -d mydb
srvctl stop instance -i mydb1
Please get an expert to perform these, especially since you want to do something with ASM. If I recall, ASM is a proprietary Oracle file system. Using srvctl would be better than trying to handle it yourself.
Here is more help on srvctl
$ srvctl stop database -h
Stops the database.
Usage: srvctl stop database -d <db_unique_name> [-o <stop_options>] [-f]
-d <db_unique_name> Unique name for the database
-o <stop_options> Options to shutdown command (e.g. normal, transactional, immediate, or abort)
-f Force stop
-h Print usage
$ srvctl stop instance -h
Stops the database instance.
Usage: srvctl stop instance -d <db_unique_name> {-n <node_name> | -i <inst_name_list>} [-o <stop_options>] [-f]
-d <db_unique_name> Unique name for the database
-n <node_name> Node name
-i "<inst,...>" Comma separated instance names
-o <stop_options> Options to shutdown command (e.g. normal, transactional, immediate, or abort)
-f Force stop
-h Print usage
$ srvctl stop asm -h
Stops ASM instance.
Usage: srvctl stop asm [-n <node_name>] [-o <stop_options>] [-f]
-n <node_name> Node name
-o <stop_options> Options to shutdown command (e.g. normal, transactional, immediate, or abort)
-f Force stop
-h Print usage
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