Originally posted by Raghubir Bose:
With vertical scaling, meaning with the addition of CPU, the performance increases , but the probability of failure does not change(neither increases or decreases).
Vertical Scaling is a very general term.
Addition of CPUs is the most popular form of vertical scaling. However there are other ways of adding hardware to increase performance.
Adding a CPU into an empty slot of a well designed multi-processor server
should not decrease reliability. In
may increase performance depending on the operational profile.
Moving from a single CPU system to a multi-CPU capable system with only one CPU equipped
could reduce reliability as there are more controllers that could fail on the multi-CPU system.
Adding a hard drive to a single hard drive system for interlaced operation
can improve performance and can be seen as vertical scaling for disk bound applications, however it will reduce reliability as a failure of either drive will be disasterous. You will have to add two more drives mirroring the first two drives to increase reliability; however your reliability
may still be below the original single drive system because of your dependence on more complex (fail-over) controllers.