ASM instance configuration and management

Staring with 10g R1 and onwards, Oracle supports two types of instances: RDBMS and ASM. An ASM instance is a special kind of instance with only Shared Global Area (SGA) that typically consists of memory components such as Shared Pool,
Large Pool, Free Memory and ASM Cache, and a set of default background process, with some additional ASM-specific background processes. The ASM instance doesn't hold any physical structure and the name of the instance typically starts with +ASM. The instance would be generally named as +ASMn (where n represents the instance number) in a cluster environment. The INSTANCE_TYPE initialization parameter controls the role played by these two instances. The ASM instance configuration
requires only a handful of initialization parameters. These parameters are discussed in the following section.

ASM instances efficiently support both non-RAC and RAC databases. Only one ASM instance is required per node, irrespective of the number of databases/instances running on the node. In an RAC environment, you need to configure one ASM
instance per node and these ASM instances across the cluster communicate with each other using an interconnected network communication. The database instances interact with the ASM instance to manage the database datafiles. ASM instances
typically listen on 1521 port by default.

ASM initialization parameters

In this section, we are going to summarize the essential ASM instance initialization parameters, their usage, and recommended values: