To understand the basic difference between “scale-up” and “scale-out” technologies, think of residential housing. You’ve got a lot of people who need shelter and minimal space constraints. A scale-up approach would be to make one building as tall as possible. However, the higher you build, the more physics and cost come into play. Soon, the economics of scaling elevation prove self-limiting, which is why fewer than a dozen buildings in the world are taller than 500 meters (1640 feet). A scale-out approach emphasizes decentralization, spreading the population among many shorter buildings. Without geographic boundary limitations, the scale-out approach will likely prove more cost-efficient and resilient against accident or attack.
Scale-out benefits, once deployed, quickly become undeniable. Unfortunately, old habits die hard, especially when capex costs have been amortized and IT budgets remain flat. Some organizations feel content to sit tight with their aging scale-up storage solutions. Many of these groups have legitimate reasons for their static strategies, but none of those reasons will dam the inexorable tide of data growth. Infrastructure built for a terabyte world will buckle in an era of petabytes. Only scale-out solutions will accommodate these rising data loads in a cost-efficient manner.
If data trends aren’t enough to persuade you that scale-up isn’t sufficient for future storage needs, consider:
- Cost. Scale-up strategy requires ever-faster hardware. In comparison, scale-out excels with cheaper, average-performance components that can be networked in massive quantities.
- Balance. In the triad of low cost, capacity, and speed, scale-up can give you capacity and speed but only with the sacrifice of low cost. Scale-out excels at capacity and offers a fair balancing of speed and cost, improving more as workloads increase.
- Ceiling. Scale-up is limited by hardware technologies and often runs up against limitations, such as the 6 Gbit/s drive interface cap. Scale-out can aggregate bandwidth for significantly higher headroom and ability to grow over time. Thus, the right software paired with the right architecture can allow scale-out to grow practically without limits.
- Upgrading. Scale-up requires “forklift upgrades,” wherein large portions of the infrastructure must be upgraded all at once. Usually, this requires knowing how much performance or capacity will be needed. A wrong guess can mean costly overprovisioning or future costs due to underprovisioning requiring another costly, large installation. Scale-out is inherently modular, allowing for the addition of just enough storage and/or servers when needed. Even if purchases result in underprovisioning, the cost of optimizing from that point will be much lower.