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ASM Related Initialization Parameters

Oracle RAC Cluster Tips by Burleson Consulting

This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters.  To get immediate access to the code depot of working RAC scripts, buy it directly from the publisher and save more than 30%.

In Oracle Database 10g some initialization parameters have been modified that control the relationship of the RAC instance with the new Oracle Database 10g Automated Storage Management interface. The modified parameters are shown in table 8.4.




This parameter allows the specification of 10g ASM disk groups using a format similar to: +dgroup2, where dgroup2 is an existing ASM disk group mounted in the nodes ASM instance.


This parameter allows the specification of ASM disk groups for recovery files location using a format similar to:  +dgroup6, where dgroup6 is an existing ASM disk group mounted in the nodes ASM instance.


This parameter specifies the size area to reserve in the db_recovery_file_dest specified disk group for recovery files. An example setting would be: 5G where 5 is the integer size and "G" in this setting tells Oracle this is gigabytes. The use of K and M are also allowed for kilobytes and megabytes.

db_create_online_log_ dest_n

This parameter (where "n" is replaced with 1-5) allows you to specify the disk group where redo logs will be created. For example specifying: +dgroup7, places the log files in ASM disk group dgroup7.

Table 8.4: ASM Initialization Parameters

By using the db_create_file_dest and db_recovery_file_dest parameters, ASM knows the disk groups on which to place the database datafiles and recovery area. This allows the DBA to simply specify create tablespace test; and the database and ASM will create a 100 megabyte file within the db_create_file_dest location, automatically striped and load balanced.

Initialization Parameters for ASM Instances

The initialization parameters in Table 8.5 relate only to an ASM instance, there will be at least one ASM instance per node in a RAC cluster. Parameters that start with ASM_ cannot be set in a normal database instance, although they will be present to the show parameter command.




In order to set the ASM parameters, this parameter must be set to instance_type = ASM. Note: This is the only required parameter. All other parameters take suitable defaults for most environments.


This parameter specifies the unique name for this group of ASM instances within the cluster or on a node. This parameter defaults to +ASM and only needs to be modified if you are trying to run multiple ASM instances on the same node.


This parameter determines the maximum power on an ASM instance for disk rebalancing operations. The default is 1, which is also the most intrusive to database operations, a higher setting makes the rebalancing operations less intrusive.


The purpose of this parameter is to limit the set of disks that Automatic Storage Management considers for discovery. If not specified the entire system is searched for compatible volumes which can lengthen startup time. The parameters default value is NULL. (This default causes ASM to find all of the disks in a platform-specific location to which it has read/write access.)


This parameter lists the names of disk groups that will be mounted by an ASM instance at startup, or when the ALTER DISKGROUP ALL MOUNT statement is issued. The parameters default value is NULL. (If this parameter is not specified, then no disk groups are mounted.) This parameter is dynamic if you are using a server parameter file (SPFILE), however you should rarely need to alter this value. ASM automatically adds a disk group to this parameter when a disk group is successfully mounted by the ASM instance, and automatically removes a disk group that is specifically dismounted. However, if you use a traditional text initialization parameter file, remember that you need to edit the initialization parameter file to add the name of any disk group that you want automatically mounted at instance startup, and remove the name of any disk group that you no longer want mounted.

Table 8.5: ASM Only Initialization Parameters

Client Side Initialization Parameter File vs. Server Parameter File

By default, Oracle uses parameter settings in the server parameter file to control database resources. The traditional client side parameter file (init.ora) can also be used; however, Oracle recommends that the server parameter file be used because it is easier to use and manage.

The server parameter file (also called SPFILE) is in a single location where all the necessary parameters are defined and stored. The defined parameter values are applicable for all the instances in the cluster. The SPFILE permits dynamic changes without requiring the instance be brought down.

The client side parameter file can still be used to manage parameter settings in Real Application Clusters; however, administrative convenience is sacrificed and the advantage of dynamic change is lost. By default, if PFILE is not specified in the STARTUP command, Oracle will use a server parameter file.


This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters, Rampant TechPress, by Mike Ault and Madhu Tumma.

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.


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