Donald K. Burleson
Oracle RAC Tips
HA systems are almost synonymous with clustered systems. In order to
minimize downtime, two or more servers, called nodes, are linked to form a
high-availability cluster system. Here are some key concepts and requirements
of HA systems:
- Automation – Fast fault detection and recovery removes time uncertainty
and contributes to a successful HA system in all environments. This process
has to be automated and it has to follow a deterministic, tested procedure.
By automating the detection and recovery process, it puts a ‘finite bound’
on the length of service outage. By not relying on manual or human
intervention, uncertainty is largely minimized.
- Redundancy - HA methodology requires a redundant set of online hardware
to effectively perform the recovery operation. HA systems rely on the
backup node to provide the same set of availability as before failure
- Fault Management software - Fault management software, consisting of a
set of deterministic routines and agents that monitor various components
such as CPU, network controller, disks units, operating system, and
database application, is required to detect the failures in a HA system.
- Design HA Environment - To achieve the desired HA effect, all relevant
environmental factors have to be analyzed and factored into the HA design.
More details on HA Clusters are covered in Chapter 3, Database Clusters.
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