Are disks the dominant contributor for storage failures?

Building reliable storage systems becomes increasingly challenging as the complexity of modern storage systems continues to grow. Understanding storage failure characteristics is crucially important for designing and building a reliable storage system. While several recent studies have been conducted on understanding storage failures, almost all of them focus on the failure characteristics of one component—disks—and do not study other storage component failures. This article analyzes the failure characteristics of storage subsystems. More specifically, we analyzed the storage logs collected from about 39,000 storage systems commercially deployed at various customer sites. The dataset covers a period of 44 months and includes about 1,800,000 disks hosted in about 155,000 storage-shelf enclosures. Our study reveals many interesting findings, providing useful guidelines for designing reliable storage systems. Some of our major findings include: (1) In addition to disk failures that contribute to 20--55% of storage subsystem failures, other components such as physical interconnects and protocol stacks also account for a significant percentage of storage subsystem failures. (2) Each individual storage subsystem failure type, and storage subsystem failure as a whole, exhibits strong self-correlations. In addition, these failures exhibit “bursty” patterns. (3) Storage subsystems configured with redundant interconnects experience 30--40% lower failure rates than those with a single interconnect. (4) Spanning disks of a RAID group across multiple shelves provides a more resilient solution for storage subsystems than within a single shelf.