Scale-up can solve a capacity problem without adding infrastructure elements such as network connectivity. However, it may require additional space, power, and cooling. Scaling up does not add controller capabilities to handle additional host activities. That means it doesn’t add costs for extra control functions.
Scale-out technology adding more disk using existing controller would not be possible, were in order to expand desired disk storage one needs to add more controller in the existing environment.
Below diagram explain the scenario correctly.
1. Scale-up solved the problem by adding extra disk (like:JBOD) in environment with existing controller.
2. Scale-out solved the problem by adding extra disk with new controller.