Some other key differences between hardware failover and Real Application Clusters
include the following:
??? The Real Application Clusters option avoids the various activities involved in
disk takeover: mounting volumes, validating filesystem integrity, opening Oracle
database files, and so on. Not performing these activities can significantly
reduce the time required to achieve full system availability.
??? The Real Application Clusters option doesn??™t require the creation and maintenance
of the complex scripts typically used to control the activities for hardware
failover. For example, there is no need to script which disk volumes will be taken
over by a surviving node. The automatic nature of Real Application Clusters avoids
the complex initial system administration to set up the failover environment, as well
as the ongoing administration needed as additional disk volumes are used. In fact,
adding disk volumes to your database but forgetting to add the volumes to the various
failover scripts can cause a hardware failover solution to fail itself!
In a simple two-way cluster used for hardware failover, both machines should have
equal processing power and should be sized so that each can handle the entire workload.
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