Hybrid Approaches for Distributed Storage Systems

Distributed or peer-to-peer storage solutions rely on the introduction of redundant data to be fault-tolerant and to achieve high reliability. One way to introduce redundancy is by simple replication. This strategy allows an easy and fast access to data, and a good bandwidth efficiency to repair the missing redundancy when a peer leaves or fails in high churn systems. However, it is known that erasure codes, like Reed-Solomon, are an efficient solution in terms of storage space to obtain high durability when compared to replication. Recently, the Regenerating Codes were proposed as an improvement of erasure codes to better use the available bandwidth when reconstructing the missing information. In this work, we compare these codes with two hybrid approaches. The first was already proposed and mixes erasure codes and replication. The second one is a new proposal that we call Double Coding. We compare these approaches with the traditional Reed-Solomon code and also Regenerating Codes from the point of view of availability, durability and storage space. This comparison uses Markov Chain Models that take into account the reconstruction time of the systems.