This is a followup to the 1994 tutorial by Berkeley RAID researchers whose 1988 RAID paper foresaw a revolutionary change in storage industry based on advances in magnetic disk technology, i.e., replacement of large capacity expensive disks with arrays of small capacity inexpensive disks. NAND flash SSDs which use less power, incur very low latency, provide high bandwidth, and are more reliable than HDDs are expected to replace HDDs as their prices drop. Replication in the form of mirrored disks and erasure coding via parity and Reed-Solomon codes are two methods to achieve higher reliability through redundancy in disk arrays. RAID(4+k), k=1,2,... arrays utilizing k check strips makes them k-disk-failure-tolerant with maximum distance separable coding with minimum redundancy. Clustered RAID, local recovery codes, partial MDS, and multilevel RAID are proposals to improve RAID reliability and performance. We discuss RAID5 performance and reliability analysis in conjunction with HDDs w/o and with latent sector errors - LSEs, which can be dealt with by intradisk redundancy and disk scrubbing, the latter enhanced with machine learning algorithms. Undetected disk errors causing silent data corruption are propagated by rebuild. We utilize the M/G/1 queueing model for RAID5 performance evaluation, present approximations for fork/join response time in degraded mode analysis, and the vacationing server model for rebuild analysis. Methods and tools for reliability evaluation with Markov chain modeling and simulation are discussed. Queueing and reliability analysis are based on probability theory and stochastic processes so that the two topics can be studied together. Their application is presented here in the context of RAID arrays in a tutorial manner.

翻译：本文是对1994年伯克利RAID研究人员教程的后续之作。他们1988年的RAID论文预言了基于磁盘技术进步而即将发生的存储行业革命性变革——即用小型廉价磁盘阵列取代大型昂贵磁盘。NAND闪存SSD功耗更低、延迟极低、带宽高，且可靠性优于HDD，随着价格下降，有望替代HDD。镜像磁盘形式的复制，以及通过奇偶校验和里德-所罗门码实现的纠删码，是通过磁盘阵列冗余实现更高可靠性的两种方法。采用k个校验条带的RAID(4+k)（k=1,2,...）阵列，利用最大距离可分编码以最小冗余实现k盘故障容错。集群RAID、本地恢复码、部分MDS以及多级RAID是提升RAID可靠性与性能的若干方案。我们讨论了结合HDD（无论是否存在潜在扇区错误LSE）的RAID5性能与可靠性分析；LSE可通过盘内冗余与磁盘清洗（后者借助机器学习算法增强）处理。未检测到的磁盘错误导致静默数据损坏，并会在重建过程中传播。我们利用M/G/1排队模型评估RAID5性能，给出降级模式下分叉/连接响应时间的近似值，以及用于重建分析的休假服务器模型。讨论了基于马尔可夫链建模与模拟的可靠性评估方法与工具。排队与可靠性分析基于概率论和随机过程，因此可将这两个主题结合研究。本文以教程形式在RAID阵列背景下展示了它们的应用。