This option can also provide additional flexibility for
scaling database applications across multiple machines, and manageability was simplified
as of Oracle Database 10g when Enterprise Manager Grid Control was introduced.
Figure 11-6. Oracle Real Application Clusters on a cluster
Oracle Instance
Database
Server
Oracle Instance
Database
Server Interconnect
Oracle Database
270 | Chapter 11: Oracle and High Availability
Real Application Clusters increases availability by enabling avoidance of complete
database blackouts. With simple hardware failover, the database is completely
unavailable until node failover, instance startup, and crash recovery are complete.
With RAC, clients can connect to a surviving instance any time. Clients may be able
to continue working with no interruption, depending on whether the data they need
to work on was under the control of the failed instance. You can think of the failure
of a Real Application Clusters instance as a potential database ???brownout,??? as
opposed to the guaranteed blackout caused by hardware failover.
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