网络存储I/O流水机制研究

将I／O请求处理划分为多个阶段，为流水线技术引入网络存储提供了新思路．同时，I／O请求处理的各阶段必定通过缓存（内存）来传递或处理数据．I／O请求处理除了直通方式外，大部分依赖存储转发方式（例如对I／O命令的聚散、排队操作等），存储转发的方式下的网络存储I／O流水线具有一些新的特点厦其自身特有的制约因素．探讨I／O流水机制，对提高网络存储系统整体性能，具有一定的指导及实践意义．     

WindowsNT环境下缓存磁盘技术驱动程序的设计与实现

随着计算机性能的迅速提高,系统越来越强烈地要求所配置的高速外存储器有更好的联机性能,I／O性能增长与CPU速度增长的严重失配,使I／O并颈问题日超严重,本文研究了Windows NT系统下的一种用来改善磁盘小写I／O（写请求的长度小于16K）性能的新途径0－缓存磁盘技术,它采用了多级Cache的存储思想,在办公／工程负载环境中的
峰值性能相对于常规磁盘有很大的提高。本文深入了研究了缓存磁盘技术在Windows NT环境下驱动程序的结构和原理,并详细阐述了具体的实现机制和方法。     

一个Linux多路径磁盘过滤驱动程序

研究Linux系统中多路径磁盘过滤驱动程序的设计和实现。驱动程序将物理磁盘的多路径封装为一个虚拟没备。虚拟设备的I／O请求转发到磁盘设备上执行，由路径选择算法将主机的负载均衡地分配到各路径上。当路径发生故障时由驱动程序将失败的I／O请求切换到其它路径，屏蔽了路径故障。驱动程序利用多路径改善了主机的I／O性能，提高了系统的可用性。     

存储区域网络中路径容错及负载均衡的研究

为利用存储区域网络的冗余路径，在主机上加入驱动程序对逻辑单元（LUN）的输入，输出请求进行截获。在故障路径上的I／O请求失败后。由驱动程序在正常路径上重新执行。路径失败时I／O请求直接发送给HBA驱动程序，避免了磁盘驱动程序中的无效重试过程，缩短了故障切换时间。I／O请求被分配到多条路径上，提高了主机的吞吐能力，缩短了I／O平均响应时间。     

SCSI冗余路径驱动程序在Windows NT下的设计和实现

该文研究了在NT系统中RDP设备驱动程序的设计原理和实现方法。RDP驱动程序通过对磁盘I/O请求的挂接和处理,实现故障切换和负载均衡。在路径发生故障时RDP驱动程序将I/O切换到其它路径,以增加系统的可用性。通过将I/O负载均衡分布在各SCSI路径,以增加系统数据吞吐能力。     

Windows磁盘缓存的优化

磁盘缓存又称为虚拟缓存,它的读／写速度比管理磁介质快得多,是改善硬盘性能的主要手段。在硬盘空闲时会把数据预先存入缓存,一旦程序请求到此段资料,可以马上从缓存中得到,无须再读／写硬盘,特别是连续存取的操作之中,Ｃａｃｈｅ能够极大地提高系统的整体速度。 Ｗｉｎｄｏｗｓ在启动时会调用一部分主内存作为磁盘缓存,而且这部分空间不再允许其它程序使用,换言之,虚拟缓存将减少可用的内存容量,影响程序的运行。实际上,磁盘缓存是由于动态和固定两部分组成的,既占用一定空间,又可以按需求变更尺寸。磁盘缓存的容量不是越大…     

一种闪存敏感的多级缓存管理方法

基于闪存的固态硬盘(solid state driver,简称SSD)已经广泛应用于各种移动设备、PC机和服务器.与磁盘相比,尽管SSD具有数据存取速度高、抗震、低功耗等优良特性,但SSD自身也存在读写不对称、价格昂贵等不利因素,这使得SSD 短期内不会完全取代磁盘.将SSD和磁盘组合构建混合系统,可以发挥不同的硬件特性,提升系统性能.基于 MLC 型 SSD 和 SLC 型 SSD 之间的特性差异,提出了一种闪存敏感的多级缓存管理策略——FAMC.FAMC将SSD用在内存和磁盘之间作扩展缓存,针对数据库系统、文件管理中数据访问的特点,有选择地将内存牺牲页缓存到不同类型的SSD.FAMC同时考虑写请求模式和负载类型对系统性能的影响,设计实现对SSD友好的数据管理策略.此外,FAMC基于不同的数据置换代价提出了适用于SSD的缓冲区管理算法.基于多级缓存存储系统对FAMC的性能进行了评测,实验结果表明,FAMC可以大幅度降低系统响应时间,减少磁盘I/O.     

Oracle基于磁盘竞争的解决方案

Oracle中磁盘竞争是影响I／O速度、降低系统性能的常见问题，可以通过分离顺序I/O、利用分片技术分散随机I／O；分别存储数据和索引、消除磁盘上的非Oracle的I／O操作、减少数据迁移和数据链接、减少碎片等方法有效地减少磁盘竞争．提高系统性能.     

内存占用与杀毒软件卡机原因详解

物理内存是计算机的主存储设备。磁盘是副存储设备，也就是说，磁盘可以不要，但是内存不能没有。内存一部分是支持CPU运算的存储空间的扩展，直接与CPU通讯（相当于低速的cache），另一部分用来存储一些常用的数据（也就是一般而言的资源），这些资源对个人电脑而言都从磁盘读取（一些工作站可以通过其余I／O设备如光盘之类的输入），所以内存也与磁盘有相当多的通讯。     

基于虚拟磁盘的文件加密方法

文件加密存储是保证机密数据不被窃取或篡改的有效方法。介绍了一种基于虚拟磁盘的文件加密方法，其思想是利用Windows WDM设备驱动程序技术，创建虚拟磁盘分区，在响应虚拟磁盘的I／O请求的过程中，进行实时的数据加／解密，并采用USB智能卡进行用户身份认证及密钥管理，从而保证存储在虚拟磁盘中的文件的安全性。实验证明，该方法是一种安全、高效、易用的文件加密存储解决方案。     

基于磁盘过滤驱动的硬盘保护技术

针对传统利用中断方式的磁盘保护有不少安全隐患,分析了一种基于磁盘过滤驱动的硬盘保护工作机制。该机制的核心思想是在对上层操作系统透明的情况下,重定向对磁盘操作的I/O请求包,在重启系统后自动清除缓存数据。由于工作在操作系统内核层增强了保护功能的安全性。     

Exploiting the performance gains of modern disk drives by enhancing data locality

Due to the widening performance gap between RAM and disk drives, a large number of I/O optimization methods have been proposed and designed to alleviate the impact of this gap. One of the most effective approaches of improving disk access performance is enhancing data locality. This is because the method could increase the hit ratio of disk cache and reduce the seek time and rotational latency. Disk drives have experienced dramatic development since the first disk drive was announced in 1956. This paper investigates some important characteristics of modern disk drives. Based on the characteristics and the observation that data access on disk drives is highly skewed, the frequently accessed data blocks and the correlated data blocks are clustered into objects and moved to the outer zones of a modern disk drive. The idea attempts to enhance spatial locality, improve the efficiency of aggressive sequential prefetch, and take advantage of Zoned Bit Recording (ZBR). An experimental simulation is employed to investigate the performance gains generated by the enhanced data locality. The performance gains are analyzed by breaking down the disk access time into seek time, rotational latency, data transfer time, and hit ratio of the disk cache. Experimental results provide useful insights into the performance behaviours of a modern disk drive with enhanced data locality.     

一种基于磁盘介质的网络存储系统缓存

随着计算规模越来越大,网络存储系统应用领域越来越广泛,对网络存储系统I/O性能要求也越来越高.在存储系统高负载的情况下,采用低速介质在客户机和网络存储系统的I/O路径上作为数据缓存也变得具有实际的意义.设计并实现了一种基于磁盘介质的存储系统块一级的缓存原型D-Cache.采用两级结构对磁盘缓存进行管理,并提出了相应的基于块一级的两级缓存管理算法.该管理算法有效地解决了因磁盘介质响应速度慢而带来的磁盘缓存管理难题,并通过位图的使用消除了磁盘缓存写Miss时的Copy on Write开销.原型系统的测试结果表明,在存储服务器高负载的情况下,缓存系统能够有效地提高系统的整体性能.     

Deconstructing on-board disk cache by using block-level real traces

On-board disk cache is an effective approach to improve disk performance by reducing the number of physical accesses to the magnetic media. Disk drive manufacturers are increasing the on-board disk cache size to match the capacity growth of the backend magnetic media. Some disk drives nowadays have a cache of 32 MB. Modern computer systems use large amounts of memory to improve performance, any data brought into host memory will be re-accessed there, not in the on-board disk cache. This feature has a significant impact on the behavior of disk cache. This is because computer systems are complex systems consisting of various components. The components are correlated with each other. Therefore, a specific component cannot be isolated from the overall system when we analyze its performance behavior. This paper employs four block-level real traces to explore the performance behavior of the on-board disk cache by considering the impacts of the cache hierarchy contained in computer systems. The analysis gives three major implications: (1) I/O stream at block-level contains negligible temporal locality. Therefore, read/write cache can only achieve marginal benefits. (2) Static write cache does not achieve performance gains since the write stream does not have too much interference with the read stream. Therefore, it is better to leave the on-board disk cache shared by both the write and read streams. (3) Read cache dominates the contribution to the hit ratio besides prefetch. Thus, it is better to focus on improving the read performance rather than write performance of disk cache.     

Profit data caching and hybrid disk‐aware Completely Fair Queuing scheduling algorithms for hybrid disks

Recently, a hybrid disk drive that integrates a small amount of flash memory within a mechanical drive has received significant attention. The hybrid drive extends the storage hierarchy by using flash memory to cache data from the mechanical disk. Unfortunately, current caching architectures fail to fully exploit the potential of the hybrid drive. Furthermore, current disk input/output (I/O) schedulers are optimized for rotational mechanical disk drives and thus must be re‐targeted for the hybrid disk drive. In this paper, we propose a new data caching scheme, called Profit Caching, for hybrid drives. Profit Caching is a self‐optimizing caching algorithm. It considers and seamlessly integrates all possible data characteristics that impact the performance of hybrid drives, including read count, write count, sequentiality, randomness, and recency, to determine the caching policy. Moreover, we propose a hybrid disk‐aware Completely Fair Queuing (HA‐CFQ) scheduler to avoid unnecessary I/O anticipations of the CFQ scheduler. We have implemented Profit Caching and HA‐CFQ scheduler in the Linux kernel. Coupled with a trace‐driven simulator, we have also conducted detailed experiments under a variety of workloads. Experimental results show that Profit Caching provides significantly improved performance compared with the previous schemes. In particular, the throughput of Profit Caching outperforms previous Random Access First and FlashCache caching schemes by factors of up to 1.8 and 7.6, respectively. In addition, the HA‐CFQ scheduler reduces the total execution time of the CFQ scheduler by up to 1.74%. Finally, the experimental results show that the runtime overhead of Profit Caching is extremely insignificant and can be ignored. Copyright © 2014 John Wiley & Sons, Ltd.     

Caching strategies to improve disk system performance

I/O subsystem manufacturers attempt to reduce latency by increasing disk rotation speeds, incorporating more intelligent disk scheduling algorithms, increasing I/O bus speed, using solid-state disks, and implementing caches at various places in the I/O stream. In this article, we examine the use of caching as a means to increase system response time and improve the data throughput of the disk subsystem. Caching can help to alleviate I/O subsystem bottlenecks caused by mechanical latencies. This article describes a caching strategy that offers the performance of caches twice its size. After explaining some basic caching issues, we examine some popular caching strategies and cache replacement algorithms, as well as the advantages and disadvantages of caching at different levels of the computer system hierarchy. Finally, we investigate the performance of three cache replacement algorithms: random replacement (RR), least recently used (LRU), and a frequency-based variation of LRU known as segmented LRU (SLRU)     

倒排文件索引缓存机制的优化

为了有效提高搜索引擎检索服务系统的整体性能,提出了一种基于倒排文件索引的缓存机制优化方法。具体研究过程是：首先分析倒排文件缓存的体系结构和数据加载,接着讨论负载数据对倒排文件缓存和缓存替换算法的影响,最后通过设计仿真实验研究倒排文件的缓存优化。研究结果表明,采用倒排文件索引的缓存机制优化方法可以明显减少磁盘系统I/O访问次数,提高磁盘系统带宽的利用率。     

并行文件系统Lustre细粒度I/O性能优化

并行文件系统Lustre粗粒度I/O性能良好,细粒度I/O性能相对粗粒度I/O比较低下,因此优化细粒度I/O性能成为提高系统整体I/O性能的关键问题。在研究和分析了Lustre的I/O访问模式、细粒度I/O服务流程和页面替换算法等方面后,提出了细粒度优先（Fine Grained First,FGF）LRU算法。在OST端及Client端的页高速缓存中最大程度地保留细粒度I/O的页面,降低细粒度I/O引起的页面下沉速度,延长细粒度I/O页面在主存中的时间,进而减少对磁盘的访问次数,降低磁盘访问开销。通过对实验数据的对比和分析,验证了FGF-LRU算法的有效性。在不影响粗粒度I/O性能的情况下,提高了细粒度I/O性能,最终实现提高系统整体I/O性能。