Erasure Coded Storage on a Changing Network: The Untold Story

As faster storage devices become commercially viable alternatives to disk drives, the network is increasingly becoming the bottleneck in achieving good performance in distributed storage systems. This is especially true for erasure coded storage, where the reconstruction of lost data can significantly encumber the system. Thus, a significant amount of research has focused on reducing the amount of data transferred during this repair process. However, in most cases the network is assumed to have a uniform static structure. One reason behind this is that many of the state of the art codes have a fixed repair mechanism or are constrained in the choice of repair strategies, therefore in theory benefit less from being network aware. We propose a general mechanism that explores the space of possible repairs and examine how much different types of erasure codes benefit by being network aware. We show significant gains for three erasure codes using both theoretical modeling and simulation results. We also consider the practical applicability of our proposed mechanism by limiting the search space to repairs that have the potential to be minimal cost and present a case study for RLNC, a class of flexible codes.