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Difference between Scale Up vs Scale Out

March 26, 2013

Scale Up: Get a Bigger Box

With this approach, you add hardware such as processors, RAM, and network interface cards to your existing servers to support increased capacity. This is a simple option and one that can be cost effective. It does not introduce additional maintenance and support costs. However, any single points of failure remain, which is a risk. Beyond a certain threshold, adding more hardware to the existing servers may not produce the desired results. For an application to scale up effectively, the underlying framework, runtime, and computer architecture must scale up as well. When scaling up, consider which resources the application is bound by. If it is memory-bound or network-bound, adding CPU resources will not help.

 

Scale Out: Get More Boxes

To scale out, you add more servers and use load balancing and clustering solutions. In addition to handling additional load, the scale-out scenario also protects against hardware failures. If one server fails, there are additional servers in the cluster that can take over the load. For example, you might host multiple Web servers in a Web farm that hosts presentation and business layers, or you might physically partition your application’s business logic and use a separately load-balanced middle tier along with a load-balanced front tier hosting the presentation layer. If your application is I/O-constrained and you must support an extremely large database, you might partition your database across multiple database servers. In general, the ability of an application to scale out depends more on its architecture than on underlying infrastructure.

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