Repair-Optimal Data Placement for Locally Repairable Codes with Optimal Minimum Hamming Distance

Modern clustered storage systems increasingly adopt erasure coding to realize reliable data storage at low storage redundancy. Locally Repairable Codes (LRC) are a family of practical erasure codes with high repair efficiency. Among various LRC constructions, Optimal-LRC is a recently proposed LRC approach that achieves the optimal Minimum Hamming Distance with low theoretical repair costs. In this paper, we consider the repair performance of Optimal-LRC in clustered storage systems. We show that the conventional flat data placement and random data placement incur substantial cross-cluster repair traffic, which impairs the repair performance. To this end, we design an optimal data placement scheme that provably minimizes the cross-cluster repair traffic, by carefully placing each group of blocks in Optimal-LRC into a minimum number of clusters subject to single-cluster fault tolerance. We implement our optimal data placement scheme on a key-value store prototype atop Memcached, and show via LAN testbed experiments that the optimal data placement significantly improves the repair performance compared to the conventional data placements.