Definition - What does Scale Out mean?
Scale out is a growth architecture or method that focuses on horizontal growth, or the addition of new resources instead of increasing the capacity of current resources (known as scaling up). In a system such as a cloud storage facility, following a scale-out growth would mean that new storage hardware and controllers would be added in order to increase capacity. This has two obvious pros – one is that storage capacity is increased and the second is traffic capacity is also increased because there is more hardware to share the load.
Techopedia explains Scale Out
Scale out is a type of capacity expansion concentrating on the addition of new hardware resources instead of increasing the capacity of already available hardware resources such as storage or processing silos. This is often used in the context of storage because ideally, it is not just the storage capacity that needs to increase in such a system, but the controller and load balancing as well. In large cloud storage systems where multitenancy and scalability are required, increasing the capacity alone in a scale-up manner would not be sufficient to handle the increasing data traffic.
The scale-up approach was an older method for growth since hardware resources were expensive, so it made sense to make the most out of existing hardware and just increase capacity. But the decreasing hardware costs has made it easier to scale out, increasing all capacities in the process.