Scale-out storage is a network-attached storage (NAS) architecture in which the total amount of disk space can be expanded as needed, even if some of the new drives reside in other storage arrays. If and when a given array reaches its storage limit, another array can be added to expand the system capacity.
Scale-out storage differs conceptually from the older scale-up approach. In a scale-up system, the network storage was confined to a single form factor, while in a scale-out system, new hardware can be added and configured as the need arises. The main advantage of the scale-out approach is cost containment, along with more efficient use of hardware resources.
Before scale-out storage became popular, enterprises often purchased storage arrays much larger than needed, to ensure that plenty of disk space would be available for future expansion. If that expansion never occurred or turned out less than expected, much of the originally purchased disk space went to waste. With the scale-out architecture, the initial investment can be more modest; if the storage requirement expands beyond expectations, new arrays can be added as needed, without limit.