What is Locally Decodable Erasure Code?

Locally Decodable erasure codes are a class of forward error-correcting codes that can reconstruct erased data, like the data on a failed drive, using only a small fraction of the surviving data strips. VAST clusters using N+4 coding can reconstruct the data from a lost drive using just 1/4th the data, and therefore 1/4th the I/Os, of a conventional erasure coding scheme.