ProactiveCache: On Reducing Degraded Read Latency of Erasure Coded Cloud Storage Erasure coding is gaining attraction in cloud storage systems because it improves data reliability with huge cost savings in terms of storage. However, data recovery in erasure codes includes high disk IO, network traffic and complex decoding that impacts degraded read latency, in case of failures. Data access latency is one of the most important metrics to determine Quality of Service. Reducing degraded latency in erasure coding is vital to improve user performance. To reduce degraded read latency of erasure codes, in this paper, we have proposed a cache based technique called ProactiveCache. This proactively copies objects in failure predicted machine into a cache tier. To deploy ProactiveCache, cloud storage system should employ various failure prediction methods to predict hardware failures. On accurate failure predictions, ProactiveCache eliminates degraded read latency. For evaluation, ProactiveCache is implemented on Ceph object storage. Experimental results show that ProactiveCache reduces degraded read latency up to 38% and improves throughput by 37%.

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.