Cloudow:一种基于用户层虚拟化的软件即服务模式运行系统

"软件即服务(SaaS)"是一种通过网络发布与使用软件的新模式,在很大程度上消除了用户购买、维护与升级应用程序的需要,被认为是软件未来的主流应用模式之一.本文提出了一种新的支持现有Windows桌面软件的SaaS模式并实现了其原型系统Cloudow:用户可以在任意的联网兼容计算机上按需运行现有的Windows软件(无需安装),且软件的个性化配置可以被保留以便下次使用时恢复.Cloudow使用用户层虚拟化技术解决了软件无需安装便能运行的问题,并通过用户层文件系统设计实现了软件在网络环境下的透明使用.与现有的基于远程虚拟机计算或者基于Web应用的SaaS模式相比,Cloudow能够直接支持现有软件的服务端存储/客户端运行模式,无需修改代码,较好地兼顾了软件兼容性与性能.同时,为尽可能降低Internet环境所带来的远程数据访问延迟,Cloudow大量采用了元数据/数据/文件预取与缓存策略,显著提高了实际部署中的应用性能;测试表明,因为采用了这些优化策略,对于很多常用的Windows桌面应用而言,在Cloudow下额外运行时间开销平均为12%到20%.     

A user-space file system for on-demand legacy desktop software

Some user-level virtualization technologies have been used to convert legacy software (like the existing Windows desktop applications) into the on-demand software without any modification. To give the client a friendly and compatible method to access on-demand legacy software across the Internet, this paper presents a clientend file system for this usage case. It is a Windows user-space file system based on the cloud storage (where the on-demand software is stored), which converts the local file system acce...     

Employing intelligence in object-based storage devices to provide attribute-based file access

Attribute-based file access has been regarded as a promising method to reach files based on their attributes rather than through the usual directory hierarchy,which is especially meaningful for locating the target among mass of files.However,because the attribute-based file system introduces higher performance overhead and is usually incompatible with existing file access interfaces,till now there are few practical attribute-based file systems.This paper designs a file system with attribute-based access methods and a compatible access interface,using object-based storage devices(OSD).In detail,this design fully utilizes existing features of the OSD standard(T10):object attributes and access methods are mapped into file attributes and the corresponding access interfaces respectively;collection-objects are used for fast indexing of user objects.Therefore,the attribute-based object organization can be achieved in OSD efficiently and the powerful processing capability of OSD is used to complete object-queries to speed up the performance.Moreover,the way to export the new accessing methods through file system with a compatible interface is also presented.Such a prototype has been implemented.Tests show that it introduces much less overheads than some existing attribute-based file systems,and the query performance is higher than its counterpart based on the block-level device.     

Size effect of layer thickness on stress fields due to interface core-spreading dislocation arrays in multilayers

The elastic fields due to interface dislocation arrays with spreading core in multilayers are derived analytically by means of the superposition of Green function of individual compact dislocations. The numerical results for Cu-Nb multilayers with dislocation arrays demonstrate that:(1) There exists a critical layer thickness(CLT) in describing interface shear stress. The maximum interface shear stress(MISS) increases with the layer thickness as it exceeds CLT; while the MISS decreases rapidly with the layer thickness as it is thinner than CLT.(2) Both the density and core width of interface dislocations have salient effect on the stress fields. The overall stress field is confined by high density of dislocations, and the stress singularity is released by core spreading.(3) A new dislocation prefers to glide in the middle region between the two adjacent interface dislocations by means of Peach-Kohler(P-K) force acting on the dislocation and elastic energy of dislocations. These findings would provide foundations to deepen the understanding of microscopic plastic deformation mechanisms and their related macroscopic mechanical properties of metallic anisotropic multilayers.