How Automatic Storage Management Works

Automatic Storage Management has a special-purpose Oracle instance, called the ASM instance, dedicated to managing disk group activity. The ASM instance manages and communicates the map as to where each file extent resides. It also controls the process of rebalancing the placement of the extents when the storage allocation is changed. As an ASM instance uses only about 64-MB for its system global area, it requires a relatively small amount of system resource. In a RAC configuration, an ASM instance on each node in the cluster manages all disk groups for that node, in coordination with the other nodes in the cluster.

Oracle Automatic Storage Management Technical Overview

Automatic Storage Management (ASM) is a new feature of Oracle Database 10g which provides a vertical integration of the file system and volume manager specifically built for the Oracle database files. ASM distributes I/O load across all available resource to optimize performance while removing the need for Manual I/O tuning (spreading out the database files avoids hot spots . ASM helps DBAs manage a dynamic database environment by allowing them to grow the database size without having to shut down the database to adjust the storage allocation.