Scalability – scale out/in vs up/down

One of important aspects of computer system is scalability. It is a capability of the system to handle expanding amount of tasks that need to be completed by the system. Prerequisite is that the system must function in same way after scaling as it was before the scaling. The system in this terms can be computer, network etc. Scalability is sometimes referred as extensibility.

There are two basic approaches to scaling of the computer systems. It is horizontal and vertical scaling.

In first case – horizontal scaling it means to add or remove a computing unit (node) to/from the system. This is so called quantitative change. As example a new computer can be added into distributed system. The horizontal scaling is also called as scale out/in.

The latter case – vertical scaling it means to change a property of the existing system by adding or removing resources to/from the computing unit (the node) of the system. This is so called qualitative change. As example it can be about adding more CPUs or memory to existing node. The vertical scaling is also called as scale up/down.

Difference between the two can be noted on following example. There can be a system of having an 8TB of memory in total in one node – a scale up approach. While as scale out example there can be 8 nodes having 1TB of memory each.

In terms of scaling of SAP HANA both approaches can be used as the HANA is designed for scale up and as well for scale out since the beginning.