Measuring the adaptability of universal accessible systems

Adaptability is a concept to improve access to content and navigation for individual users of information systems in various settings of interaction. Following the usability-engineering tradition to provide operational definitions of principles, and subsequently to develop techniques for evaluation based on these definitions, we revisited adaptability concepts and designed a structured technique (     

Measuring the adaptability of universal accessible systems

Adaptability is a concept to improve access to content and navigation for individual users of information systems in various settings of interaction. Following the usability-engineering tradition to provide operational definitions of principles, and subsequently to develop techniques for evaluation based on these definitions, we revisited adaptability concepts and designed a structured technique (     

硬件实现RAID与软件实现RAID的比较

现在的服务器中存在多种RAID实现方式,RAID系统提供了数据冗余备份功能,能帮助预防信息丢失.本文讨论了硬件RAID和软件RAID实现的差异和性价比的权衡.并分析了对系统性能的影响,以便帮助管理员了解哪种RAID实现方式最能满足他们的需求.     

RAID-VCR:一种能够承受三个磁盘故障的RAID结构

提出了一种新RAID结构——RAID-VCR.这种结构仅需要3个额外的磁盘来保存校验信息,但是却能够承受任意模式的3个成员磁盘故障.与现有的其它RAID结构相比,RAID-VCR的容灾能力大幅提高,但是对磁盘空间利用率和系统吞吐量的影响却非常小.RAID-VCR的编码和解码过程都是基于简单的XOR操作,并且以明文方式保存了用户数据,从而可以高效地执行读操作.仿真实验结果表明,RAID-VCR的编码和解码性能较好,具有很好的应用前景.     

Hobbes Framework—an adaptable solution to web-driven applications

Adaptability of software systems is of serious concern to practitioners. Loosely speaking, adaptability could be defined as the ability of a system to accommodate varying user requirements with little to no intervention from the developer. Implementing adaptability in web-based systems, however, poses challenges of its own. Web-based applications are usually large (in terms of components, lines of code, etc.), complex, and utilize numerous software packages usually supplied by different third-party vendors. It will be very useful to the software engineering community if an adaptable framework is available that can be quickly tailored to today's demanding software requirements, and be easy to re-use. In this paper, a framework is presented, called the Hobbes Framework (HF) that has helped solve many of the current challenges regarding adaptability. HF has been used extensively in two major web-based projects and is currently being implemented in another. HF has proven highly adaptable to varying project and user requirements.     

磁盘阵列多终端管理系统的设计与实现

针对用户对磁盘阵列多样性配置方式的需求,设计了一种可支持多终端并发操作的磁盘阵列管理系统。该系统利用分层架构思想实现,并进行了三点改进:第一,将队列管理加入到分层设计中,避免了系统升级带来的级联变更;第二,利用XML文档组织队列消息,增强了消息管理的灵活性,提高了系统开发的并行度;第三,利用XML为用户界面建模,实现了界面的"零编码"开发。因此,利用改进后的分层架构,使得系统具有较好的可扩展性、可维护性以及开发简单的特点。     

RAID0.5: design and implementation of a low cost disk array data protection method

RAID has long been established as an effective way to provide highly reliable as well as high-performance disk subsystems. However, reliability in RAID systems comes at the cost of extra disks. In this paper, we describe a mechanism that we have termed RAID0.5 that enables striped disks with very high data reliability but low disk cost. We take advantage of the fact that most disk systems use offline backup systems for disaster recovery. With the use of these offline backup systems, the disk system needs to only replicate data since the last backup, thus drastically reducing the storage space requirement. Though RAID0.5 has the same data loss characteristics of traditional mirroring, the lower storage space comes at the cost of lower availability. Thus, RAID0.5 is a tradeoff between lower disk cost and lower availability while still preserving very high data reliability. We present analytical reliability models and experimental results that demonstrate the enhanced reliability and performance of the proposed RAID0.5 system.     

SA3—a tool for supporting adaptable software architecture generation for embedded systems

Adaptability is emerging as an important attribute or nonfunctional requirement (NFR) for embedded systems. Intuitively, adaptability is the ability of a software system to accommodate changes in its environment. However, in order for the embedded system to be adaptable its architecture, the first step in the development, should itself be adaptable. It will be helpful if the generation of this architecture could be automated. In this paper, we describe a tool called the Software Architecture Adaptability Assistant (SA³) that helps generate adaptable architectures. SA³ uses the properties of the NFR Framework, in particular its knowledge base properties, to create a catalog of various constituents of architecture such as components and connections, and then searches the catalog to find adaptable constituents for the architecture. In this paper, we describe the theory behind SA³ and then describe the tool itself. We then demonstrate the architecture generation capability of the tool for embedded systems. We also discuss why these architectures are adaptable as well as point out directions for further improvement.     

IP-SAN环境下RAID远程管理系统设计与实现

针对IP-SAN存储网络中磁盘阵列的实时管理需求，设计并实现了磁盘阵列的远程管理系统。该远程管理系统采用标准的客户辫抄服务器模式，结合Web动态交互技术、session技术、用户访问控制和面向对象的CGI编程等，使远程管理系统具有高效性和稳定性。利用该远程管理系统可以通过Web实时进行磁盘阵列的状态查看，逻辑磁盘分区，逻辑卷（分区）导出等操作，有效地提高了IP-SAN的存储管理性能。     

基于IOP321的嵌入式RAID系统中的硬异或实现

为提高RAID系统的可靠性,RAID3/5/6算法在数据写入的过程中采用异或运算产生奇偶校验信息。当RAID出现故障时,也是通过异或运算完成数据的重构。因此,异或运算是RAID系统工作时频繁而且重要的操作之一。本文详细介绍了采用Intel IOP321处理器的应用加速单元实现异或运算的工作原理和软件模块设计,并通过实验测试证明,专门的硬异或单元比嵌入式处理器做软件异或运算的速度快7倍以上,有效地解决了嵌入式环境下异或的性能瓶颈问题。     

一种新型的能够防止两块磁盘失败的技术

海量存储系统的建设是目前计算机系统最热门和发展最快的领域,存储系统的主要部分是在线存储系统。RAID(磁盘阵列)对于提升存储系统的效率、数据的高可靠性、防止数据破坏和业务停顿具有重大意义。目前实际应用中的RAID 1,RAID 0+1,RAID 4,RAID 5都只能防止单块磁盘的损坏,实际生产中已经出现了很多由于双盘损坏造成业务长时间停顿的事故。在介绍了通用的RAID级别的基础上,介绍了一种新型的对角线奇偶校验方法,结合水平奇偶校验,可以防止两块磁盘损坏。通过可靠的数学分析,可以看到该方法可以极大提高磁     

廉价冗余盘阵列(RAID)发展综述

廉价冗余盘阵列（ＲＡＩＤ）因为能够有效提高计算机数据传输率和数据可靠度,已经成为计算机外存储系统的重要组成部分。近年来,为了进一步提高ＲＡＩＤ的请求响应时间和数据可靠度,改善ＲＡＩＤ性能,涌现了多种新技术。文章针对ＲＡＩＤ性能的各个方面,对这些新技术进行了详细介绍。     

面向普适计算的自适应软件模型及平台实现

适应性是普适计算软件的主要特征。现有研究工作在模型和体系结构层面上缺乏对软件自适应的内在抽象,因而很难为自适应软件的建模、开发和运行提供全面支撑。针对现有研究工作存在的不足,首先以适应性为核心,提出了自主单元的概念及其构件化参考实现模型,用统一的、具有适应能力的自主单元来对普适计算实体进行抽象和描述;进而提出基于自主单元的自适应软件体系结构,从概念、开发和运行3个层面对其进行了系统化阐述,并且实现了支撑该体系结构、基于微内核架构的普适计算软件平台UbiStar;最后以智能博物馆应用为典型案例,对自主单元模型和UbiStar平台的有效性进行了验证。     

RAID中Cache的设计与实现

在RAID（廉价冗余磁盘阵列）系统的开发中,Cache的设计是重要一环,它的效率直接影响到了RAID系统的性能,本文首先介绍了Cache的原理和常用的一些技术,并比较了它们的优缺点,然后针对RAID系统的实际情况,介绍了RAID中Cache的设计和实现。     

RAID系统的面向对象建模

廉价磁盘冗余阵列RAID系统的使用,较好的解决了计算机的I／O瓶颈问题。由于RAID系统本身的复杂性,传统的结构化分析方法已无法提供对系统全面正常的描述,而面向对象方法良好的封装性和重用性,能使系统的复杂性在一定内得以降低。本文以RAID控制系统的软件设计为背景,采用UML的面向对象可视化设计方法,从概念视图、静态视图和动态视图等多个视角,讨对RAID控制系统的建模、分析和实现。     

使用备份加速RAID5数据重构

对于大部分中小企业,为了保证生产系统所存放数据的安全,通常使用RAID5和备份两种技术.提出了一种新型的RAID5加速重构模型,该模型具有以下优点:1)能够灵活整合生产系统和备份系统;2)充分利用备份系统的资源,加速生产系统内RAID5数据重构;3)改善生产系统服务质量;4)提高生产系统的可靠性和可用性.     

面向多应用环境RAID系统的智能预取和缓存调度

本文分析了RAID系统的多应用环境数据请求的存储模式的特点，提出了能根据应用环境的不同而自动改变预取策略的智能预取算法以及缓存调度算法。实践证明，本算法使得RAID系统的预取和缓存调度摆脱了盲目性，保证了预取策略和缓存调度的最优性。     

CSWL: Cross-SSD Wear-Leveling Method in SSD-Based RAID Systems for System Endurance and Performance

Flash memory has limited erasure/program cycles.Hence,to meet their advertised capacity all the time,flashbased solid state drives(SSDs) must prolong their life span through a wear-leveling mechanism.As a very important part of flash translation layer(FTL),wear leveling is usually implemented in SSD controllers,which is called internal wear leveling.However,there is no wear leveling among SSDs in SSD-based redundant array of independent disks(RAIDs) systems,making some SSDs wear out faster than others.Once an SSD fails,reconstruction must be triggered immediately,but the cost of this process is so high that both system reliability and availability are affected seriously.We therefore propose cross-SSD wear leveling(CSWL) to enhance the endurance of entire SSD-based RAID systems.Under the workload of random access pattern,parity stripes suffer from much more updates because updating to a data stripe will cause the modification of other all related parity stripes.Based on this principle,we introduce an age-driven parity distribution scheme to guarantee wear leveling among flash SSDs and thereby prolong the endurance of RAID systems.Furthermore,age-driven parity distribution benefits performance by maintaining better load balance.With insignificant overhead,CSWL can significantly improve both the life span and performance of SSD-based RAID.     

RAID技术实现及发展

首先介绍了RAID技术的发展和重要意义,对当今业界应用的各种RAID级的优缺点进行了比较,并简述RAID5技术实现方法,最后介绍新一代RAID技术标准.     

分布式RAID中Cache模块的设计

针对分布式RAID的特殊架构，设计了基于总线侦听方法的Cache模块。该模块采用主存分块映射策略来解决总线侦听方法，由于共享网络总线对带宽要求太高，使用较少带宽、较少的数据操作，提高了分布式RAID的系统性能。对Cache模块设计进行了性能分析，对多处理机系统Cache一致性问题的解决方案进行了分析比较。