Oracle Tips by Burleson

Oracle10g Grid Computing with RAC
Chapter 5 - Preparing Shared Storage

ASM Instances

ASM instances are not used to mount databases, they are simply used to coordinate data layout for database instances. However, the database instances do direct I/O to disks in disk groups. I/O doesn't go through the ASM instance.

ASM instances cannot mount a database; they mount disk groups. An ASM instance must be started before a database instance can access files in disk groups. Multiple and separate database instances can share disk groups for their files. On a single node, a single ASM instance typically manages all disk groups. In a Real Application Cluster environment, each node typically has one ASM instance that manages all disk groups for that node in a coordinated manner with the rest of the cluster.

All ASM management commands are directed through the ASM instance, no ASM commands are issued to any regular Oracle database instance using the ASM files.

ASM Instance Background Processes

There are at least two new background processes added for an ASM instance: