Database Reference
In-Depth Information
Application
Application
Application
Single Client Access Name (SCAN)
RAC Node1
VIP
VIP
Service
Service
Listener
Listener
RAC Database Instance
Private
Interconnect
RAC Database Instance
Grid Infra structure
Grid Infra structure
ASM
Clusterware
Clusterware
ASM
OperatingSystem
Operating System
OCR/
Voting disk
RAC
Database
Figure 1-3.
Oracle RAC architecture and components
Grid Infrastructure: Oracle Clusterware and ASM
Clusterware is a layer of software that is tightly integrated with the OS to provide clustering features to the RAC
databases on a set of servers. Before Oracle 9i, Oracle depended on OS vendors or third-party vendors to provide
the Clusterware solution. In Oracle 9i, Oracle released its own clusterware on Linux and Windows, and in Oracle
10g Oracle extended its clusterware to other OS. Oracle Clusterware was significantly enhanced in 11g. In 11gR2,
Oracle combined Clusterware and Oracle ASM into a single product called Grid Infrastructure. Oracle Clusterware is
required software to run the Oracle RAC option, and it must be installed in its own, nonshared Oracle home. Usually
we have a dedicated OS user “grid” to own Grid Infrastructure as well as Oracle ASM instance, which is different from
the Oracle RAC database owner “oracle.”
Oracle Clusterware serves as a foundation for Oracle RAC Database. It provides a set of additional processes
running on each cluster server (node) that allow the cluster nodes to communicate with each other so that these
cluster nodes can work together as if they were one server serving the database users. This infrastructure is necessary
to run Oracle RAC.
During Grid Infrastructure installation, ASM instances, database services, and virtual IP (VIP) services, the
Single Client Access Name (SCAN), SCAN listener, Oracle Notification Service (ONS), and the Oracle Net listener
are configured and also registered as Clusterware resources and managed with Oracle Clusterware. Then, after you
create a RAC database, the database is also registered and managed with Oracle Clusterware. Oracle Clusterware is
responsible for starting the database when the clusterware starts and restarting it once if fails.
Oracle Clusterware also tracks the configuration and status of resources it manages, such as RAC databases, ASM
instances, database services, listeners, VIP addresses, ASM diskgroups, and application processes. These are known
as Cluster Ready Service (CRS) resources. Oracle Clusterware checks the status of these resources at periodic intervals
and restarts them a fixed number of times (depending on the type of resource) if they fail. Oracle Clusterware stores
