Scale-up , Scale-out , Why Deploy RAC？

Scale-Up
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If you can achieve greater throughout over a fixed period of time by increasing the amount of parallelism, it is known as scale-up. Scale-up is achieved by increasing the amount of hardware resoruces, such as processors and memory, available within a single system image.

Scale-out
in a clustered environment it is possible to add hardware resources by adding another node. this is known as Scalue-out.

why Deploy RAC?
RAC can be a complex and costly technology to implement. It requires higher levels of skill and experience to architect, install, configure, tune, and support.

Most user implement RAC to achieve either higher availability, greater scalability, or a combination of these.

---pro oracle database 1og RAC on Linux