Scale-out versus Scale-up

Introduction

Scaling up and scaling out are two IT strategies that both increase the processing power and storage capacity of systems. The difference is in how engineers achieve this type of growth and system improvement. The terms "scale up" and "scale out" refer to the way in which the infrastructure is grown.

While scaling out involves adding more discrete units to a system in order to add capacity, scaling up involves building existing units by integrating resources into them.

One of the easiest ways to describe both of these methods is that scaling out generally means building horizontally, while scaling up means building vertically. 

Scale Out

Scaling out takes the existing infrastructure, and replicates it to work in parallel. This has the effect of increasing infrastructure capacity roughly linearly. Data centers often scale out using pods. Build a compute pod, spin up applications to use it, then scale out by building another pod to add capacity. Actual application performance may not be linear, as application architectures must be written to work effectively in a scale-out environment.

Scale Up

Scaling up is taking what you’ve got, and replacing it with something more powerful. From a networking perspective, this could be taking a 1GbE switch, and replacing it with a 10GbE switch. Same number of switchports, but the bandwidth has been scaled up via bigger pipes. The 1GbE bottleneck has been relieved by the 10GbE replacement.

Scaling up is a viable scaling solution until it is impossible to scale up individual components any larger.