You will have to weigh the cost of high availability (or the lack thereof) compared to
the increased cost and slight increase in maintenance of a RAC.
I
Chapter 10: Real Application Clusters 351
NOTE
A ???stretch cluster???, or a cluster using RAC technology over a wide-area
network (WAN), protects against the loss of an entire data center, but
it increases the cost of the infrastructure, since the already-redundant
storage systems must be duplicated across the sites and the network
bandwidth must be high enough to keep up with synchronization
tasks during peak transaction periods.
In the next few sections, we??™ll cover some of the hardware and software requirements for a
RAC database as well as detail the network configuration and disk storage requirements to build
a successful cluster.
Hardware Configuration
A complete discussion of all possible RAC hardware configurations is beyond the scope of this
book. You want to have at least two and preferably three nodes for a RAC, each with redundant
power supplies, network cards, dual CPUs, and error-correcting memory; these are desirable
characteristics for any type of server, not just an Oracle server! The higher the number of nodes
configured in the cluster, the lower the performance hit you will take when one of the cluster??™s
nodes fails.
The shared disk subsystem should also have hardware redundancy built in??”multiple power
supplies, RAID-enabled disks, and so forth.
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