I believe many of you aware about great Eric Brewer theorem which says that any networked shared-data system can have only two of three desirable properties: Consistency or high Availability or tolerance to network Partitions (i.e. this property means that network may loose any packet/message ) – this theorem usually called CAP-theorem. This theorem is quite important (or even very fundamental) for many distributed workloads like computational and data grids and “2 of 3” principle is basis for many architectural decisions in cloud world. Below I combine couple of great links around that topic which surely may shred some light on that principle as well as give you more insights how that basic rule is changed nowadays . And yes, by the way CAP theorem is key thing for most of NoSQL or any other data distributed solutions – below you might good reading about that topic, including some new views on that topic.