Balancing Repair Bandwidth and Sub-Packetization in Erasure-Coded Storage via Elastic Transformation.

Erasure coding provides high fault-tolerant storage with significantly low redundancy overhead, at the expense of high repair bandwidth. While there exist access-optimal codes that theoretically minimize both the repair bandwidth and the amount of disk reads, they also incur a high sub-packetization level, thereby leading to non-sequential I/Os and degrading repair performance. We propose elastic transformation, a framework that transforms any base code into a new code with smaller repair bandwidth for all or a subset of nodes, such that it can be configured with a wide range of sub-packetization levels to limit the non-sequential I/O overhead. We prove the fault tolerance of elastic transformation and model numerically the repair performance with respect to a sub-packetization level. We further prototype and evaluate elastic transformation atop HDFS, and show how it reduces the single-block repair time of the base codes and access-optimal codes in a real network setting.