Using ASM with RAC
The Database Configuration Assistant (DBCA) is used
in Oracle Database 10g to configure the Automated Storage Management
(ASM) features for conventional and Real Application Clusters (RAC)
environments. ASM is used to automate and simplify the optimal layout of
datafiles, control files, and log files.
Oracle created Automatic Storage Management (ASM)
as an alternative to raw devices and 3rd party clusterware
(Veritas Cluster Filesystem) for Oracle Real Application Cluster (RAC)
databases. Managing raw devices with the native "pp" commands are
cumbersome, but you need to understand that while ASM has become the
de-facto standard for Oracle, the use of ASM in RAC is somewhat
different.
For complete details on the nuances of using ASM
with RAC, I recommend the book
Oracle
Grid & Real Application Clusters.
In order to use the ASM in a shared mode for the
use of RAC database, an ASM instance needs to be created for each node
of the RAC database involving the same disk devices as input. Each ASM
instance has either an SPFILE or PFILE type parameter file. To use ASM
in the RAC environment we recommend the
svrctl commands as opposed to the Oracle GUI.
ASM provides a vertical integration of the file
system and volume manager for Oracle database files. ASM has the
capability to spreads database files across all available storage for
optimal performance and resource utilization. It enables simple and
non-intrusive resource allocation and provides automatic rebalancing
Using ASM for building shared files would get almost the same
performance as that of raw partitions. The ASM controlled disk devices
will be part of ASM instance which can be shared by the RAC database
instance.
When using ASM with RAC, it's critical to "load
balance" the ASM diskgroups by functional area. One of the largest
RAC performance problems relate to cross-node sharing of common data,
and my segregating ASM diskgroups by functional area you can greatly
reduce cache fusion overhead. For example, you want to create ASM
groups for finance data, another for inventory data, and then map the
users from those departments to those ASM disk groups via a dedicated
node.
