A Large-Scale Study of Flash Memory Failures in the Field

Abstract

Servers use flash memory based solid state drives (SSDs) as a high-performance alternative to hard disk drives to store persistent data. Unfortunately, recent increases in flash density have also brought about decreases in chip-level reliability. In a data center environment, flash-based SSD failures can lead to downtime and, in the worst case, data loss. As a result, it is important to understand flash memory reliability characteristics over flash lifetime in a realistic production data center environment running modern applications and system software. This paper presents the first large-scale study of flash-based SSD reliability in the field. We analyze data collected across a majority of flash-based solid state drives at Facebook data centers over nearly four years and many millions of operational hours in order to understand failure properties and trends of flash-based SSDs. Our study considers a variety of SSD characteristics, including: the amount of data written to and read from flash chips; how data is mapped within the SSD address space; the amount of data copied, erased, and discarded by the flash controller; and flash board temperature and bus power. Based on our field analysis of how flash memory errors manifest when running modern workloads on modern SSDs, this paper is the first to make several major observations: (1) SSD failure rates do not increase monotonically with flash chip wear; instead they go through several distinct periods corresponding to how failures emerge and are subsequently detected, (2) the effects of read disturbance errors are not prevalent in the field, (3) sparse logical data layout across an SSD's physical address space (e.g., non-contiguous data), as measured by the amount of metadata required to track logical address translations stored in an SSD-internal DRAM buffer, can greatly affect SSD failure rate, (4) higher temperatures lead to higher failure rates, but techniques that throttle SSD operation appear to greatly reduce the negative reliability impact of higher temperatures, and (5) data written by the operating system to flash-based SSDs does not always accurately indicate the amount of wear induced on flash cells due to optimizations in the SSD controller and buffering employed in the system software. We hope that the findings of this first large-scale flash memory reliability study can inspire others to develop other publicly-available analyses and novel flash reliability solutions.

Reliability of NAND Flash Memories: Planar Cells and Emerging Issues in 3D Devices

“…In the following, however, we will go beyond the manufacturer specifications and look at the basic physical mechanisms at the heart of the reliability issues. Since this is an extremely large field, we restrict our discussion to issues that develop with memory usage, neglecting for example defect-related issues, time-zero problems such as V T placement, cell-to-cell interference and many others, for which we refer the reader to other overviews of Flash memory reliability that are available in the literature, leaning either toward a device/technology [27,[51][52][53][54][55][56][57][58][59] or user [60][61][62] viewpoint.…”

“…It has also been found [262] that repeated RD on partially-programmed blocks leads to an increased BER when the remaining pages are programmed, suggesting that extensive RD can lead to a degradation of the program characteristic of the cell. In any case, it has been claimed [61] that RD errors are not the prevalent ones in SSDs used in servers. …”

Cloud Computing - Current Status and Future Directions

“…SSD prices are dropping and they continue to replace disk storage [118], and high-speed persistent memory is expected to become practical soon. Interconnects between processors are also expected to increase in speed.…”

Effects of prolonged media usage and long-term planning on archival systems

“…A recent Facebook study [40] showed that SSDs using flash memory do not degrade monotonically as flash wears but go through several distinct periods, depending on when failures emerge and are detected, and the effect of read disturbance is not the predominant source of errors in SSDs. This study was done on the use of SSDs for hot data, which lends support to our claim that extending service life of SSDs should be cost efficient in an archival setting.…”