Plane级的闪存固态盘并行调度算法

为有效缓解固态盘的存储瓶颈问题,针对闪存固态盘内部芯片的工作原理和物理特性,将并行调度技术引入闪存固态盘的闪存转换层(FTL)的设计中,设计并实现了一种plane级的并行调度算法,基本方法就是将一个读写请求分解成多个段,在多个plane上并行的执行,通过更均衡的分配I/O负载,可以显著提高闪存固态盘的整体读写性能。通过设置不同的芯片参数进行了模拟与测试,实验结果表明,采用并行调度技术可以有效提高闪存固态盘中存储芯片之间的并行度,以及芯片内部各个单元之间的并行度,闪存固态盘的读写延时均有较大改善。     

WAPFTL:支持预测机制的负载自适应闪存转换层算法

基于NAND Flash的固态盘凭借其低延迟、低功耗、高可靠性等优点,已经开始应用于企业级服务器和高性能计算领域。针对固态盘相对较差的写性能及使用寿命有限等不足,提出了一种闪存转换层中基于页映射机制的自适应地址映射算法WAPFTL。该算法能够在地址转换过程中预测负载读写特性并自适应地调整地址映射信息缓存的策略。实验结果表明,WAPFTL能够高效协同利用负载的时间局部性和空间局部性,提高地址映射命中率,减少因地址映射而引起的额外写操作次数;同时,有效减少了垃圾回收次数,提高了SSD整体性能。     

Integrated write buffer management for solid state drives

NAND flash memory-based Solid State Drives (SSD) have many merits, in comparison to the traditional hard disk drives (HDD). However, random write within SSD is still far slower than sequential read/write and random read. There are two independent approaches for resolving this problem as follows: (1) using overprovisioning so that reserved portion of the physical memory space can be used as, for example, log blocks, for performance enhancement, and (2) using internal write buffer (DRAM or Non-Volatile RAM) within SSD. While log blocks are managed by the Flash Translation Layer (FTL), write buffer management has been treated separately from the FTL. Write buffer management schemes did not use the exact status of log blocks, and log block management schemes in FTL did not consider the behavior of the write buffer management scheme. This paper first demonstrates that log blocks and write buffers maintain a tight relationship, which necessitates integrated management to both of them. Since log blocks can also be viewed as another type of write buffer, we can manage both of them as an integrated write buffer. Then we propose an Integrated Write buffer Management scheme (IWM), which collectively manages both the write buffer and log blocks. The proposed scheme greatly outperforms previous schemes in terms of write amplification, block erase count, and execution time.     

TridentFS: a hybrid file system for non‐volatile RAM,flash memory and magnetic disk

A hybrid file system with high flexibility and performance, called Trident file system (TridentFS), is proposed to manage three types of storage with different performance characteristics, that is, Non‐Volatile RAM (NVRAM), flash memory and magnetic disk. Unlike previous NVRAM‐based hybrid file systems, novel techniques are used in TridentFS to improve the flexibility and performance. TridentFS is flexible by the support of various forms of flash memory and a wide range of NVRAM size. The former is achieved on the basis of the concept of stackable file systems, and the latter is achieved by allowing data eviction from the NVRAM. TridentFS achieves high performance by keeping hot data in the NVRAM and allowing data evicted from the NVRAM to be parallel distributed to the flash memory and disk. A data eviction policy is proposed to determine the data to be evicted from the NVRAM. Moreover, a data distribution algorithm is proposed to effectively leverage the parallelism between flash memory and disk during data distribution. TridentFS is implemented as a loadable module on Linux 2.6.29. The performance results show that it works well for both small‐sized and large‐sized NVRAM, and the proposed eviction policy outperforms LRU by 27%. Moreover, by effectively leveraging the parallelism between flash memory and disk, the proposed data distribution algorithm outperforms the RAID‐0 and a size‐based distribution method by up to 471.6% and 82.6%, respectively. By considering the data size and performance characteristics of the storage, the proposed data distribution algorithm outperforms the greedy algorithm by up to 15.5%. Copyright © 2014 John Wiley & Sons, Ltd.     

Flash存储中间层技术的研究

针对Flash存储器特殊的硬件特性和编程特性,提出了在其底层驱动和上层应用之间增加一个中间层（Logical Disk System,LDS）。LDS屏蔽了Flash的硬件特性,间接实现了擦写平衡。LDS的核心是block映射机制。文中介绍了block映射机制的物理块状态管理、物理块逻辑关系管理、映射关系表管理、垃圾回收机制等关键技术。最后通过一个实例对LDS进行性能分析,验证了该方法在实际应用中的可行性。     

基于NAND闪存的固态盘技术研究

基于NAND闪存的固态盘具有非易失、访问速度快、体积小、抗震性好以及功耗低等诸多优点,能较好缓解I/O性能瓶颈问题,已经成为学术界和产业界关注的一个研究热点.对基于NAND闪存固态盘的主要热点问题予以研究,介绍了基于闪存固态盘的技术特性,分析了其内部结构,对其关键实现技术着重进行了研究分析.     

POS产品中Flash Memory和电池测试软件设计

随着移动计算技术的发展和移动信息交换的日益频繁,闪存（Flash Memory）和电池也成为这些产品中不可缺少的组成部分。描述了一种用于闪存和电池测试的具体设计方案,侧重测试软件部分,主要包括总体设计思想和软件规划指标;介绍了各模块工作原理,以及各主要芯片如KU80L188ECl3、MBM30LV0064、XC9572XL等。     

基于NAND闪存存储器的一种超级块闪存翻译层机制研究

NAND闪存的存储系统中,软件中间层闪存翻译层通常被用来隐藏写前必须先擦除的NAND闪存特性。介绍一种新的闪存翻译层机制,它会将相邻的逻辑块合并为一个块,称之为超级块,该超级块在闪存翻译层机制下是粗颗粒度映射,而其中的页是被细颗粒度映射到物理块的任意位置。为了减少额外的存储和闪存操作,细颗粒度映射信息被保存在NAND闪存的空闲区域。使用该混合映射技术不仅具有细颗粒度的灵活性而且只需要占用粗颗粒度的存储空间。实验结果研究表明,与其他闪存翻译层技术相比,该闪存翻译层机制减少了多达40%的垃圾回收操作。     

一种高效的星载高速固态存储器坏块管理算法

随着卫星技术的发展和功能的多样化,星载固态存储器需要存储的数据量越来越大,存储速率越来越高,在轨寿命越来越长。基于NAND Flash的星载固态存储器的并行存储方案得到广泛应用。但是由于NAND Flash存在初始坏块,且Flash芯片中坏块分布离散性较大。当固态存储器存储速率较高,并行存储的Flash芯片数增多,坏块经叠加映射后,使固态存储器有效容量损失较大。针对高速固态存储器的坏块问题,提出了一种高效的坏块管理算法,通过对坏块进行地址映射和替换,使固态存储器初始有效容量与装机容量的比值在高速并行存储的情况下仍能保持在97%左右,提高了Flash芯片存储容量的利用率,延长了大容量星载高速固态存储器的使用寿命。     

FeGC: An efficient garbage collection scheme for flash memory based storage systems

NAND flash memory is a promising storage media that provides low-power consumption, high density, high performance, and shock resistance. Due to these versatile features, NAND flash memory is anticipated to be used as storage in enterprise-scale systems as well as small embedded devices. However, unlike traditional hard disks, flash memory should perform garbage collection that consists of a series of erase operations. The erase operation is time-consuming and it usually degrades the performance of storage systems seriously. Moreover, the number of erase operations allowed to each flash memory block is limited. This paper presents a new garbage collection scheme for flash memory based storage systems that focuses on reducing garbage collection overhead, and improving the endurance of flash memory. The scheme also reduces the energy consumption of storage systems significantly. Trace-driven simulations show that the proposed scheme performs better than various existing garbage collection schemes in terms of the garbage collection time, the number of erase operations, the energy consumption, and the endurance of flash memory.     

基于队列计数的固态存储器热数据识别方法*

目前较常用的热数据识别方法主要关注于数据的访问频繁度,却没有有效地体现出访问次数随时间的变化关系,从而造成了较高的错误识别率。针对这种不足,设计了基于队列计数的热数据识别方法,通过使用先进先出规则淘汰过时的数据,并赋予队列中每个位置所存放元素不同的权值来表示不同时刻各数据的热状态;同时结合Flash读写等特性,引入了热区域概念,使其所需存储空间大大降低。通过理论分析以及实验证明,此方法在热数据识别和均衡效果方面达到了较好的性能,从而提高了垃圾回收的效率以及延长了存储器的使用寿命。     

基于逻辑区间热度的NAND闪存垃圾回收算法

针对现有的NAND闪存垃圾回收算法中回收性能不高,磨损均衡效果差,并且算法内存开销大的问题,提出了一种基于逻辑区间热度的垃圾回收算法。该算法重新定义了热度计算公式,把连续逻辑地址的NAND内存定义为一个热度区间,以逻辑区间的热度来代替逻辑页的热度,并将不同热度的数据分开存储到不同擦除次数的闪存块上,有效地实现了数据冷热分离,并且节约了内存空间。同时,算法还构造了一种新的回收代价函数来选择回收块,在考虑回收效率的同时,还兼顾了磨损均衡的问题。实验结果表明,该算法与性能优异的FaGC算法相比,总的擦除次数减少了11%,总的拷贝次数减少了13%,擦次数最大差值减少了42%,内存消耗能减少了75%。因此,该算法有利于增加闪存可用空间,改善闪存系统的读写性能,延长闪存使用寿命。     

基于固定内存和状态管理的模型检测方法*

在研究固定内存和状态管理的基础上,提出了一种新的模型检测方法,使得在任何计算机上都能对任意规模的并发系统进行模型检测.     

Exploring optimal combination of a file system and an I/O scheduler for underlying solid state disks

Performance and energy consumption of a solid state disk （SSD） highly depend on file systems and I/O schedulers in operating systems. To find an optimal combination of a file system and an I/O scheduler for SSDs, we use a metric called the aggregative indicator （AI）, which is the ratio of SSD performance value （e.g., data transfer rate in MB/s or throughput in IOPS） to that of energy consumption for an SSD. This metric aims to evaluate SSD performance per energy consumption and to study the SSD which delivers high performance at low energy consumption in a combination of a file system and an I/O scheduler. We also propose a metric called Cemp to study the changes of energy consumption and mean performance for an Intel SSD （SSD-I） when it provides the largest AI, lowest power, and highest performance, respectively. Using Cemp, we attempt to find the combination of a file system and an I/O scheduler to make SSD-I deliver a smooth change in energy consumption. We employ Filebench as a workload generator to simulate a wide range of workloads （i.e., varmail, fileserver, and webserver）, and explore optimM combinations of file systems and I/O schedulers （i.e., optimal values of AI） for tested SSDs under different workloads. Experimental results reveal that the proposed aggregative indicator is comprehensive for exploring the optimal combination of a file system and an I/O scheduler for SSDs, compared with an individual metric.     

Distributed extended state observer design and output feedback anti-disturbance control for nonlinear interconnected systems: A dynamic memory event-triggered mechanism

This paper investigates a distributed extended state observer design and output feedback anti-disturbance control for nonlinear interconnected systems (ISs) with multiple disturbances. First, a distributed extended state observer with a sparse observer communication network is established to estimate the system states and external disturbances. Then, an output feedback controller with a disturbance compensation (DC) item is designed, where a novel dynamic memory event-triggered mechanism (DMETM) is proposed to save communication resources. Third, under the proposed controller, the closed-loop signals are bounded and the system states and the estimation errors converge to zero. Additionally, the system outputs satisfy $$ performance. Finally, the simulation examples demonstrate the effectiveness of the DMETM in reducing the number of data transmissions compared to the dynamic event-triggered mechanism (ETM).     

A hybrid fault prediction method for control systems based on extended state observer and hidden Markov model

Fault diagnosis and prediction for complex control systems rely either on the collection of rich data for training neural networks or on the system models and prior knowledge of faults. These methods are difficult to apply directly in complex integrated systems due to the large uncertainties in practical scenarios. A new fault diagnosis and prediction technique that is based on extended state observer (ESO) and a hidden Markov model (HMM) for control systems is proposed in this paper. Real-time and predictive information that is obtained by ESO of the active disturbance rejection control (ADRC) is utilized to improve the HMM method for the fault prediction of control systems with large uncertain disturbances. The proposed approach realizes a high recognition rate with a small demand for data, and the dependence on the system model is weak without prior knowledge of faults. Fault prediction of the control system output can be realized without additional sensors. The proposed solution is evaluated in simulations of an asynchronous servo motor control system against the traditional control method and the ADRC control. The results indicate that the proposed method performs well in fault prediction and outperforms the traditional method in terms of control when disturbances and failures occur.