If you want High Availability for free, you will have to look into shared nothing architectures. You have open source solutions such as Sequoia (http://sequoia.continuent.org) that are database neutral that can do the job. Live migration is doable with shared nothing but it will take longer (basically depends on the size of your VM size).

The post surprisingly does not mention Aster Data Systems which is the datawarehouse behind MySpace. When web sites start to store and analyze every single user click then you quickly get into massive amount of data. It's no surprise that the Petabyte barrier is reached especially with the density of storage increasing at constant cost.