Large-scale storage systems increasingly adopt era-sure coding for low-cost reliable storage by storing stripes of data and parity blocks. To further achieve higher storage savings with performance guarantees, enterprises and academia explore wide stripes with locally repairable codes (LRCs). However, how to efficiently generate wide LRC stripes remains a non-trivial issue. Current approaches on stripe merging provide a starting point for merging narrow LRC stripes into wide LRC stripes, but they lack flexibility in the number of stripes being merged and the stripe width of the wide LRC stripes being formed. In this paper, we propose staged stripe merging for wide stripe generation in LRCs, by allowing a flexible number of narrow LRC stripes to be gradually merged into a wide stripe in multiple stages with optimality guarantees. In particular, we design an optimal data placement scheme for a group of narrow LRC stripes to be merged, such that it provably minimizes the cross-cluster network traffic for stripe merging across each stage, while maintaining the repair efficiency of LRCs. We implement the optimal data placement scheme for two production LRC constructions in a distributed storage prototype. Evaluation shows that our optimal data placement scheme significantly reduces the stripe merging time compared with several baselines.

Large-scale storage systems increasingly deploy erasure coding to provide high-reliability and low-cost data storage. To achieve further storage savings while maintaining repair efficiency, enterprises and academia explore wide stripes using locally repairable codes (LRCs) and several constructions are proposed. However, we find that these wide stripe LRCs neglect the file access information within the stripe, which matters as these LRCs assign uniform local group sizes while a wide stripe comprises many files with non-uniform or skewed access frequencies. Consequently, the repair efficiency is compromised. To this end, we design a novel wide stripe LRC construction called non-uniform LRC by fully considering the skewed file accesses in a wide stripe. Our non-uniform LRC assigns small group sizes for hot files in the stripe to achieve low repair cost and large group sizes for cold files to realize low storage overhead. It performs well under general coding parameters, adapts to irregular file sizes, provides high fault tolerance, and can be flexibly deployed to various data placements in real-world clustered storage systems. We implement our non-uniform LRC in a distributed storage prototype. Evaluations show that it greatly reduces the degraded read time and improves the node repair rate compared with the state-of-the-art wide stripe LRCs.