Observation and Optimization on Garbage Collection of Flash Memories: The View in Performance Cliff

Abstract

The recent development of 3D flash memories has promoted the widespread application of SSDs in modern storage systems by providing large storage capacity and low cost. Garbage collection (GC) as a time-consuming but necessary operation in flash memories largely affects the performance. In this paper, we perform a comprehensive experimental study on how garbage collection impacts the performance of flash-based SSDs, in the view of performance cliff that closely relates to Quality of Service (QoS). According to the study results using real-world workloads, we first observe that GC occasionally causes response time spikes, which we call the performance cliff problem. Then, we find that 3D SSDs exacerbate the situation by inducing a much higher number of page migrations during GC. To relieve the performance cliff problem, we propose PreGC to assist normal GC. The key idea is to distribute the page migrations into the period before normal GC, thus leading to a reduction in page migrations during the GC period. Comprehensive experiments with real-world workloads have been performed on the SSDsim simulator. Experimental results show that PreGC can efficiently relieve the performance cliff by reducing the tail latency from the 90th to 99.99th percentiles while inducing a little extra write amplification.

Editorial for the Special Issue on Flash Memory Devices

“…This Special Issue provides insight on and advancements in Flash memory devices. There are nine papers including one review paper, covering the reliability of 3D NAND Flash devices [1][2][3], the characterization and design of Flash memory cell/string [2,4,5], NOR Flash memories for embedded applications [5], a set of Error Correction Codes and Secondary Correction Algorithms for flash memories [6,7], Flash management through flash signal processing in controllers for Big Data storage [6][7][8], and the impact of Flash memories on Solid State Drives reliability and performance [8,9].…”

“…The method has been validated on commercial off-the-shelf TLC 3D NAND Flash memory. In [9], Du et al defined garbage collection (GC) as a time-consuming but necessary operation in Flash memories. They performed a comprehensive experimental study in view of a performance cliff that closely relates to Quality of Service (QoS).…”