Oh I am absolutely aware that erasure codes are an old thing, Reed-Solomon codes exist since the 1960's, but this is not simply a trivial application of erasure coding to a storage system: erasure codes alone don't provide the same durability guarantees that replication does. [0]
This is a combination of erasure coding AND replication, whose combined storage amplification is dramatically lower than previous SOTA.
I gave a longer explanation in a sibing comment to yours [1]
[0] http://fireless.cs.cornell.edu/publications/erasure_iptps.pd...