NAND flash memory is being widely used as data storage in consumer electronics devices such as tablet computers and smartphones. However, due to the inherent nature of NAND flash memory where in-place update is not supported, NAND flash-based SSDs (Solid-State Drives) suffer from severe performance degradation as they need to move valid data during garbage collection (GC). Recently, multi-streamed SSDs have been proposed to reduce the cost of GC in the SSDs. However, commercial SSDs used in consumer electronics devices support only a small number of streams due to the device’s limitation in hardware resources. This makes it difficult to fully utilize the benefits of the multi-streamed SSDs. In this article, we propose a new concept of virtual streams ( vStreams ) that are independent of the number of available streams within the multi-streamed SSDs. We present the design and implementation of virtual stream management architecture, called vStream-FTL, for efficient stream management in the SSD. Specifically, we present novel mechanisms to monitor the lifetime of each stream with a negligible memory overhead and map one or more vStreams into a physical stream at run time according to the lifetime of vStream. In addition, we implement the enhanced garbage collection scheme, called vStream-aware GC that increases the benefits of multi-streamed SSDs further. Our vStream-FTL allows embedded system developers to manage a sufficient number of streams regardless of the physical streams supported by the device. The evaluation results with smartphone workload show that the proposed vStream-FTL improves throughput by 48% compared to the Legacy-FTL with no stream support.

中文翻译：

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基于NAND闪存的虚拟流管理的设计与实现

NAND闪存被广泛用作诸如平板电脑和智能手机之类的消费电子设备中的数据存储。但是，由于不支持就地更新的NAND闪存的固有特性，基于NAND闪存的SSD（固态驱动器）由于在垃圾回收（GC）期间需要移动有效数据而遭受严重的性能下降。近来，已经提出了多流SSD以降低SSD中GC的成本。但是，由于硬件资源的限制，消费类电子设备中使用的商用SSD仅支持少量流。这使得难以充分利用多数据流SSD的优势。在本文中，我们提出了一个新的概念虚拟流 （ 流 ），而不依赖于多数据流SSD中的可用数据流数量。我们介绍了称为vStream-FTL的虚拟流管理体系结构的设计和实现，以实现SSD中的高效流管理。具体来说，我们提出了新颖的机制来以可忽略的内存开销监视每个流的生存期，并根据vStream的生存期在运行时将一个或多个vStream映射到物理流中。此外，我们实施了增强的垃圾收集方案，称为支持vStream的GC这进一步增加了多数据流SSD的优势。我们的vStream-FTL允许嵌入式系统开发人员管理足够数量的流，而与设备支持的物理流无关。智能手机工作负载的评估结果表明，与不支持流的Legacy-FTL相比，建议的vStream-FTL将吞吐量提高了48％。