Enabling I/O-Efficient Redundancy Transitioning in Erasure-Coded KV Stores via Elastic Reed-Solomon Codes

Modern key-value (KV) stores increasingly adopt erasure coding to reliably store data. To adapt to the changing demands on access performance and reliability requirements, KV stores perform redundancy transitioning by tuning the redundancy schemes with different coding parameters. However, redundancy transitioning incurs extensive I/Os, which impair the performance of KV stores. We propose a new family of erasure codes, called Elastic Reed-Solomon (ERS) codes, whose primary goal is to mitigate I/Os in redundancy transitioning. ERS codes eliminate data block relocation, while limiting I/Os for parity block updates via the new co-design of encoding matrix construction and data placement. We realize ERS codes as a KV store atop Memcached, and show via LAN testbed experiments that ERS codes significantly reduce the latency of redundancy transitioning compared to state-of-the-arts.