[adrianratnapala]

If a terabyte is a lot of data to you -- and it is for many, many things, then this post is right; you should buy as much RAM as you have data, and access it accordingly.

The commenters who are saying disk has a different price/performance trade-off that is still valuable are also right, but that applies to large data sets.

[AndyNemmity]

I worked on a petabyte in memory hana cluster. It all depends on what you're doing, and how important it is to you.

I don't even know what a large data set is anymore. I think my general definition is one you won't put into memory, whatever your threshold is for that.