9.3. Defining ASM Initialization Parameters

A number of initialization parameters either are specific to ASM instances or have new values within an ASM instance. An SPFILE is highly recommended over an initialization parameter file for an ASM instance. For example, parameters such as ASM_DISKGROUPS are automatically maintained when a disk group is added or dropped, potentially freeing you from ever having to manually change this value.

These initialization parameters include the following:

INSTANCE_TYPE

For an ASM instance, the INSTANCE_TYPE parameter has a value of ASM. The default, for a traditional Oracle instance, is RDBMS.

DB_UNIQUE_NAME

The default value for the DB_UNIQUE_NAME parameter is +ASM and is the unique name for a group of ASM instances within a cluster or on a single node. The default value needs to be modified only if you're trying to run multiple ASM instances on a single node.

ASM_POWER_LIMIT

To ensure that rebalancing operations do not interfere with ongoing user I/O, the ASM_POWER_LIMIT parameter controls how fast rebalance operations occur. The values range from 1 to 11, with 11 being the highest possible value; the default value is 1 (low I/O overhead). Because this is a dynamic parameter, you may set this to a low value during the day and set it higher overnight whenever a disk rebalancing operation must occur.

ASM_DISKSTRING

The ASM_DISKSTRING parameter specifies one or more strings, which are operating system dependent, to limit the disk devices that can be used to create disk groups. If this value is NULL, all disks visible to the ASM instance are potential candidates for creating disk groups.

Here is the value for the development server:

SQL> show parameter asm_diskstring

NAME                 TYPE      VALUE
----------------------- ----------- ------------------
asm_diskstring       string    /dev/raw/*

When creating disk groups, the only disks available on this server are raw disks.

ASM_DISKGROUPS

The ASM_DISKGROUPS parameter specifies a list containing the names of the disk groups to be automatically mounted by the ASM instance at startup or by the ALTER DISKGROUP ALL MOUNT command. Even if this list is empty at instance startup, any existing disk group can be manually mounted.

LARGE_POOL_SIZE

The LARGE_POOL_SIZE parameter is useful for both regular and ASM instances. However, this pool is used differently for an ASM instance. All internal ASM packages are executed from this pool, so this parameter should be set to at least 8MB.