Chameleon: An Adaptive Wear Balancer for Flash Clusters

NAND flash-based Solid State Devices (SSDs) offer the desirable features of high performance, energy efficiency, and fast growing capacity. Thus, the use of SSDs is increasing in distributed storage systems. A key obstacle in this context is that the natural unbalance in distributed I/O workloads can result in wear imbalance across the SSDs in a distributed setting. This, in turn can have significant impact on the reliability, performance, and lifetime of the storage deployment. Extant load balancers for storage systems do not consider SSD wear imbalance when placing data, as the main design goal of such balancers is to extract higher performance. Consequently, data migration is the only common technique for tackling wear imbalance, where existing data is moved from highly loaded servers to the least loaded ones. In this paper, we explore an innovative holistic approach, Chameleon, that employs data redundancy techniques such as replication and erasure-coding, coupled with endurance-aware write offloading, to mitigate wear level imbalance in distributed SSD-based storage. Chameleon aims to balance the wear among different flash servers while meeting desirable objectives of: extending life of flash servers; improving I/O performance; and avoiding bottlenecks. Evaluation with a 50 node SSD cluster shows that Chameleon reduces the wear distribution deviation by 81% while improving the write performance by up to 33%.

基于NAND的基于Flash的固态设备（SSD）提供了高性能，能源效率和快速增长能力的理想特征。因此，在分布式存储系统中，SSD的使用正在增加。在这种情况下，一个关键的障碍是，分布式I/O工作负载的自然不平衡会导致在分布式设置中跨SSD的磨损不平衡。反过来，这可能会对存储部署的可靠性，性能和寿命产生重大影响。存储系统的现有负载平衡器在放置数据时不会考虑SSD磨损不平衡，因为此类平衡器的主要设计目标是提取更高的性能。因此，数据迁移是解决磨损不平衡的唯一常见技术，其中现有数据从高度负载的服务器转移到负载最少的服务器。在本文中，我们探索了一种创新的整体方法，即Chameleon，该方法采用了数据冗余技术，例如复制和擦除编码，再加上耐力 - 吸引意识的注销卸载，以减轻基于分布式SSD的存储中的磨损水平不平衡。 Chameleon旨在平衡不同的闪存服务器之间的磨损，同时达到理想的目标：延长闪光灯的寿命；提高I/O性能；并避免瓶颈。使用50个节点SSD群集的评估表明，变色龙将磨损分布偏差降低了81％，同时将写入性能提高了33％。