Cost follows complexity, even if it's not always immediately obvious.
A 1TB RAM server is more expensive than 10x 100GB RAM servers, but the hardware cost is often small compared to the business and technical cost of getting a solution to scale across a cluster.
Of course, generalizations are always dangerous—the take-home point here is perhaps that before going to a cluster because “that's the way big data is handled,” it's a good idea to do a proper cost-benefit analysis.
A 1TB RAM server is more expensive than 10x 100GB RAM servers, but the hardware cost is often small compared to the business and technical cost of getting a solution to scale across a cluster.
Of course, generalizations are always dangerous—the take-home point here is perhaps that before going to a cluster because “that's the way big data is handled,” it's a good idea to do a proper cost-benefit analysis.