ASM Architecture
For certain database operations like file
creation, ASM intervention is required and the database
foreground connects directly to the ASM instance. Whenever a
connection is made to the ASM instance, the OSMB process is
started dynamically. Database instances are only allowed to
connect to one ASM instance at a time, so they have at most one
OSMB background process.
Like RAC, the ASM instances themselves may
be clustered using the existing Global Cache Services (GCS)
infrastructure. There
is usually one ASM instance per node on a cluster. As with
existing RAC configurations, ASM requires that the Operating
System make ASM
instance on that node.
A basic
component of Automatic Storage Management is the disk group.
ASM is configured
by
creating disk groups, which in database instances can be used as
the default location for files created in the database. Oracle
provides SQL statements to create and manage disk groups, their contents, and
their metadata.
Group services are used to register the
connection information needed by the database instances to find
ASM instances. Group Services are a part of Oracle’s portable
clusterware, which gets automatically installed on every node
that runs Oracle10g. ASM eliminates the need for manual disk
tuning.
The ASM hierarchy can be explained using a
diagram. Compare it with previous versions of Oracle databases.
Figure 5.1 Automatic Storage Management
Hierarchy
