Question: What are the best options for a geographically distributed disaster recovery using RAC? Can I use Data Guard or Streams for disaster recovery?
Answer: Yes, you can always use Streams or Data Guard for Disaster recovery, but if you have a distance of less than 90 miles, you can use a geographically distributed RAC cluster.
For distributed RAC you need a super-fast interconnect (e.g. "dark fiber" fiber channel connectivity) you can have geographically distributed RAC nodes, but a more common alternative to extended RAC is to use Data Guard or Streams (n-way replication) for disaster recovery.
For shops with high capital funding (lotsa cash), you can employ Dense Wavelength Division Multiplexing (DWDM) technology or dark fiber, but it becomes very expensive over long geographical distances.
The choice depends mostly on costs and the volume of updates (DML) for the RAC cluster, plus your tolerance for unplanned outages during a disaster. For enough money, you can guarantee continuous availability with extended RAC clusters, but if you can afford a 30 minute downtime, Data Guard or n-way Streams may be a better approach
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