Optimistic Erasure-Coded Distributed Storage

We study erasure-coded atomic register implementations in an asynchronous crash-recovery model. Erasure coding provides a cheap and space-efficient way to tolerate failures in a distributed system. This paper presents ORCAS, Optimistic eRasure-Coded Atomic Storage, which consists of two separate implementations, ORCAS-A and ORCAS-B. In terms of storage space used, ORCAS-A is more efficient in systems where we expect large number of concurrent writes, whereas, ORCAS-B is more suitable if not many writes are invoked concurrently. Compared to replication based implementations, both ORCAS implementations significantly save on the storage space. The implementations are optimistic in the sense that the used storage is lower in synchronous periods, which are considered common in practice, as compared to asynchronous periods. Indirectly, we show that tolerating asynchronous periods does not increase storage overhead during synchronous periods.