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RAC means we run a >3 node cluster as active-active oracle instances mounting the same database. RAC runs a heartbeat across the cluster and links a virutal IP with each node in the cluster. If any host or database fails in the cluster the VIP of the corresponding node fails over to a surviving node in the cluster. As soon as all the clients connected to the failed node retry the connection they get a immediate rejection since the VIP has failed over and they can get a new connection from a surviving node immediately. This failover happens within seconds. RAC can be implemented in current infrastructure on VM's over NFS with Netapp.
ab) Dataguard with FSFO (Fast Start Fail Over)
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