Oracle ASM is typically installed in an Oracle Grid Infrastructure home separate from the Oracle Database home. Only one Oracle ASM instance is supported on a server in a standard configuration; however, Oracle Flex ASM provides additional configuration options.
Initialization Parameters and Oracle ASM Instance Creation
The initialization parameters that are of specific interest for an ASM instance are:
INSTANCE_TYPE– Set to ASM or RDBMS depending on the instance type. The default is RDBMS.
DB_UNIQUE_NAME– Specifies a globally unique name for the database. This defaults to +ASM but must be altered if you intend to run multiple ASM instances.
ASM_POWER_LIMIT-The maximum power for a rebalancing operation on an ASM instance. The valid values range from 1 to 11, with 1 being the default. The higher the limit the more resources are allocated resulting in faster rebalancing operations. This value is also used as the default when the
POWERclause is omitted from a rebalance operation.
ASM_DISKGROUPS– The list of disk groups that should be mounted by an ASM instance during instance startup, or by the
ALTER DISKGROUP ALL MOUNTstatement. ASM configuration changes are automatically reflected in this parameter.
ASM_DISKSTRING– Specifies a value that can be used to limit the disks considered for discovery. Altering the default value may improve the speed of disk group mount time and the speed of adding a disk to a disk group. Changing the parameter to a value which prevents the discovery of already mounted disks results in an error. The default value is NULL allowing all suitable disks to be considered.
Incorrect usage of parameters in ASM or RDBMS instances result in ORA-15021 errors.
To create an ASM instance first create a file called “init+ASM.ora” in the “/tmp” directory containing the following information.
Next, using SQL*Plus connect to the ide instance.
export ORACLE_SID=+ASM sqlplus / as sysdba
Create an spfile using the contents of the “init+ASM.ora” file.
SQL> CREATE SPFILE FROM PFILE='/tmp/init+ASM.ora'; File created.
Finally, start the instance with the
SQL> startup nomount ASM instance started Total System Global Area 125829120 bytes Fixed Size 1301456 bytes Variable Size 124527664 bytes Database Buffers 0 bytes Redo Buffers 0 bytes SQL>
The ASM instance is now ready to use for creating and mounting disk groups. To shutdown the ASM instance issue the following command.
SQL> shutdown ASM instance shutdown SQL>
Once an ASM instance is present disk groups can be used for the following parameters in database instances (
INSTANCE_TYPE=RDBMS) to allow ASM file creation:
Startup and Shutdown of ASM Instances
ASM instance are started and stopped in a similar way to normal database instances. The options for the
STARTUP command are:
FORCE– Performs a
SHUTDOWN ABORTbefore restarting the ASM instance.
MOUNT– Starts the ASM instance and mounts the disk groups specified by the
NOMOUNT– Starts the ASM instance without mounting any disk groups.
OPEN– This is not a valid option for an ASM instance.
The options for the
SHUTDOWN command are:
NORMAL– The ASM instance waits for all connected ASM instances and SQL sessions to exit then shuts down.
IMMEDIATE– The ASM instance waits for any SQL transactions to complete then shuts down. It doesn’t wait for sessions to exit.
TRANSACTIONAL– Same as
ABORT– The ASM instance shuts down instantly.