GRPU: An Efficient Graph-based Cross-Rack Parallel Update Scheme for Cloud Storage Systems

Erasure coding (EC) has been widely used in cloud storage systems to provide both high reliability and low storage cost. Previous literatures show that the cross-rack update operations are prevalent for many applications in erasure-coded cloud storage systems, which introduces significant I/O amplification, load imbalance and high latency. Several existing methods have been proposed to mitigate these problems. However, they ignore the correlations among chunks when performing data placement. Thus numerous stripes and racks participate in the update leading to extra I/Os and cross-rack traffic. Moreover, they don’t take into account the parallelism of network transmission which loses the potential update performance gains.To address the issues, we propose a novel Graph-based cross-Rack Parallel Update (GRPU) scheme to improve the update performance for erasure-coded cloud storage systems. The key idea of GRPU is to place the correlated chunks in the same stripe and rack, and transmit the chunks in parallel based on the network distance. The data placement and transmission paths selection are guided by two kinds of graphs. To demonstrate the effectiveness of GRPU, we conduct several experiments in a local cluster. The results show that, compared to the state-of-the-art methods, GRPU reduces the cross-rack traffic by up to 34.66% and the average response time by up to 61.69%, respectively.