StorageReliabilityRepair TradeOffs in Distributed Storage System For reliability purpose, data redundancy is anessential in distributed storage system. In the evolving of data redundancy schemes, storagereliabilityrepair tradeoffs always exist. From replication to erasure codes, higher reliability achieves with lower storage cost, but the higher repair penalty can not be ignored. Optimized data redundancy schemes like regenerating codes or basic pyramid codes are proposed to relieve the high repair penalty. In order to study the storagereliabilityrepair tradeoffs, we propose a new model based on the standard Markov Chain, it takes the irregular fault tolerance, latent sector error and correlated failures into account, and measures the storage and repair cost from system perspective. Through interscheme and intrascheme discussions, we find some principles about choosing data redundancy schemes and corresponding parameters to achieve better storagereliabilityrepair tradeoffs. Our goal is to provide system designers and administrators with concrete information to help them achieve proper storagereliabilityrepair tradeoffs.

Storage and repair bandwidth tradeoff for heterogeneous cluster distributed storage systems The storage and repair bandwidth tradeoff is an important issue in distributed storage systems (DSSs) where large scale data are stored in multiple nodes with erasure coding to ensure reliability. There are lots of studies on the DSS model with multiple clusters where the repair bandwidths from intracluster and crosscluster nodes are differentiated to improve repair efficiency based on the realistic network topological structures. At the same time, separate nodes are also prevalent due to the variety of practical networks, but the work on the cluster DSS model with multiple separate nodes is insufficient, which is a main motivation of this paper. We formulate the tradeoff bound between storage repair bandwidth for a heterogeneous DSS model consisting of clusters and separate nodes by analyzing the mincuts of heterogeneous information flow graphs corresponding to the orders of failed nodes. Additionally, the tradeoff bounds are investigated in multiple aspects when the repair bandwidth constraints and the amount of separate nodes vary, respectively. Moreover, a class of regenerating codes are illustrated to achieve the tradeoff in the heterogeneous cases.