Erasure-Coded Byzantine Storage with Separate Metadata
  Although many distributed storage protocols have been introduced, a solution that combines the strongest properties in terms of availability, consistency, fault-tolerance, storage complexity and the supported level of concurrency, has been elusive for a long time. Combining these properties is difficult, especially if the resulting solution is required to be efficient and incur low cost. We present AWE, the first erasure-coded distributed implementation of a multi-writer multi-reader read/write storage object that is, at the same time: (1) asynchronous, (2) wait-free, (3) atomic, (4) amnesic, (i.e., with data nodes storing a bounded number of values) and (5) Byzantine fault-tolerant (BFT) using the optimal number of nodes. Furthermore, AWE is efficient since it does not use public-key cryptography and requires data nodes that support only reads and writes, further reducing the cost of deployment and ownership of a distributed storage solution. Notably, AWE stores metadata separately from $k$-out-of-$n$ erasure-coded fragments. This enables AWE to be the first BFT protocol that uses as few as $2t+k$ data nodes to tolerate $t$ Byzantine nodes, for any $k \ge 1$. 
Elli Androulaki, Christian Cachin, Dan Dobre, Marko Vukolic
cs.DC