Locality and availability in distributed storage

This paper studies the problem of code symbol availability: a code symbol is said to have (r; t)-availability if it can be reconstructed from t disjoint groups of other code symbols, each of size at most r. For example, 3-replication supports (1; 2)-availability as each symbol can be read from its t = 2 other (disjoint) replicas, i.e., r = 1. However, the rate of replication must vanish like 1 over t+1 as the availability increases.