The term scale-out is used in server and storage technology for the expansion of their architectures. It is about adapting the computing power of the servers or adapting the storage capacity to the increasing customer demand.
When scaling out servers, the server infrastructure is expanded by similar servers. This can involve the expansion of a server farm in which each server supports a specific application, but it can also involve the establishment of a cluster infrastructure in which one application requires the entire available computing capacity, for example for technical-scientific calculations.
The scale-out of modular storage architectures is about adapting storage capacity to the growing volume of data. In this technique, storage space is used across hard disks. In contrast to scale-out, scale-up involves upgrading individual servers.