[angrybits]

Single-server relational backends can survive loads well in excess of most of us will ever see for our software. There are a handful of truly web-scale companies that need specialized engineering, and the time to solve for that is when you actually have that problem in sight. Conforming SQL engines can do some amazing things with simple and declarative code, giving that up in the hopes you might be Twitter-scale one day is, in my opinion, a quite poor tradeoff.

[Arkadir]

I certainly agree that most people who pick NoSQL solutions "for scalability" never add a third server to their cluster.

[joevandyk]

Amazon offers 1-8 800 GB SSD drives in their i2 instances. RAIDing them together gives you pretty awesome performance and space.