基于预拷贝的虚拟机动态内存迁移机制改进

针对内存预拷贝过程中迁移时间较长和内存页反复重传的特点,改进传统的内存动态迁移机制,引入马尔科夫预测模型,提出基于脏页概率预测的工作集测定算法.利用脏页的历史操作访问情况预测其下一轮迭代被修改的概率,只传输预测概率较低的页.实验结果表明,该算法缩短了迁移总时间和停机时间,能有效支持虚拟机动态迁移.     

改进的内存预拷贝动态迁移算法

由于预拷贝迁移算法的迭代拷贝过程存在重复地拷贝同一个内存页的问题,从而导致拷贝内存页数量的增加和总迁移时间的延长。对脏页拷贝策略进行改进,将修改频繁的脏页在停机拷贝阶段传输,从而有效地缩短总迁移时间。然而该策略的改进又导致停机拷贝阶段的页面增多而引起停机时间延长,于是采用LZO压缩算法将停机阶段待拷贝的页面先压缩再传输,通过降低待传输的数据量来缩短停机时间。在进行虚拟机迁移实验时,与预拷贝迁移算法相比,结果表明该算法在未延长停机时间的同时,缩短了总迁移时间,尤其是在高脏页率环境下,该算法明显表现出更优的迁移性能。     

基于内存迭代拷贝的Xen虚拟机动态迁移机制研究

为减少虚拟机动态迁移时间,Xen采用了Pre-Copy算法来选择合适的时间进行停机拷贝,以保证在低负载或空负载时的虚拟机迁移的优越性能,但在高负载环境下,Pre-Copy算法对内存页的重复迭代严重影响了虚拟机迁移的效率。基于Xen虚拟机内存迭代拷贝算法,提出了一种内存分片迭代拷贝机制,即通过缩短迭代拷贝的终止时间来减少虚拟机动态迁移所花费的时间。实验结果表明,内存分片迭代机制可以有效提升Xen虚拟机动态迁移的性能。     

基于内存关联分析的预拷贝迁移优化策略

内存预拷贝迁移在密集型负载下存在内存脏页反复传输的问题,导致迭代轮数较多且大幅降低了内存预拷贝迁移的整体性能。脏页概率预测能够有效减少内存脏页反复传输的现象,然而现有脏页概率预测研究都只关注时间相关性而未考虑内存之间的空间相关性。针对该问题,提出一种基于内存关联分析的预拷贝迁移策略。通过脏页率对脏页下一轮变脏概率进行预测,设计Memory_cor算法计算出脏页的关联规则和关联内存页,避免变脏概率大的内存页及其关联内存页传输。实验结果表明,该策略在总迁移时间和停机时间上优于Xen预拷贝迁移方法。     

虚拟机实时迁移中自适应阈值机制的研究

虚拟化的数据中心主要采用预拷贝(Pre-copy)算法进行虚拟机实时迁移.当虚拟机中运行负载较高或者网络传输带宽较低时,预拷贝算法固定的停机阈值严重影响实时迁移的性能.针对这个问题,提出一种自适应停机阈值机制,根据之前各拷贝轮中脏页率构成的时间序列,首先利用动态指数平滑法来预测后轮的脏页率,在预测脏页率超过网络传输带宽的情况下,再采用Mann-Kendall检验模型对脏页率变化趋势进行判断,根据判断结果确定停机切换的时机.实验结果证明,采用基于自适应阈值机制的预拷贝算法能在高负载低延迟场景下有效提高实时迁移性能.     

Xen下虚拟机动态迁移优化策略的研究

尽管预拷贝技术由于其毫秒级的停机时间及对应用影响较小而被广泛使用到各大虚拟化平台的内存数据迁移中,但是当网络处于低带宽高负载的情况下则会导致虚拟机服务的一些性能下降。为了解决以上问题,本文首先将传统的预拷贝机制与马尔科夫模型结合旨在对后轮脏页率进行预测,利用Mann-Kendall检验模型对迁移中脏页率的变化趋势进行判断,据此引入自适应阈值机制确定最优迁移策略,更好地解决虚拟机中网络传输带宽的大小和运行负载的高低对传统预拷贝技术固定停机阈值机制的影响,实验结果显示,改进后的迁移机制可有效地提高虚拟机实时迁移性能。     

面向业务特征的自适应虚拟机迁移带宽分配算法

虚拟机动态迁移是支持绿色云计算环境的重要技术,迭代时间和宕机时间是迁移性能的衡量指标,而虚拟机迁移时使用的网络带宽和业务运行产生的内存脏页是影响迁移性能的重要因素,因此合理分配迁移带宽和减少脏页率能够有效缩短迭代时间和宕机时间.该文提出了一种面向业务特征的自适应虚拟机迁移带宽分配算法,通过对迁移过程中脏页率的分析,预测运行业务的网络带宽使用量,自适应分配虚拟机迁移带宽;引入带宽调整系数,有效处理迁移过程中的业务数据抖动现象,从而确保预测的合理性.这一算法能够在保证迁移性能和系统可靠性的同时,减少迭代时间和宕机时间.实验表明在带宽资源有限的前提下,该方法能够合理利用空闲带宽资源,提高迁移性能,确保业务服务质量.     

基于虚拟机执行过程重放的热迁移系统研究

为解决传统的基于检查点和内存预拷贝的系统热迁移在一些特定环境下存在停机时间过长的问题,提出了一种基于虚拟机执行过程迭代重放的备份热迁移方案,并对迁移过程中的开销较大的检查点设置操作进行了优化.与传统迁移方法进行量化比较分析结果表明,该方案缩短了检查点设置的停机时间,传输数据量更少,从而缩短了虚拟机迁移过程总的停机时间,为低速网络带宽的迁移环境提供了更好的解决方案.     

基于服务活跃度的虚拟机实时迁移方案的研究

虚拟机实时迁移是在保证虚拟机服务正常运行的同时,在不同的物理主机之间迁移,为保证迁移效率和服务正常运行,需降低总迁移时间和停机时间。后拷贝和预拷贝是常用的两种实时迁移方案,后拷贝能降低总迁移时间,预拷贝能降低停机时间。基于服务活跃度的预拷贝优化方案是根据服务活跃度选择合适的停止条件,使得虚拟机在合适的临界点进入停机阶段,这不仅减少了页的迭代次数,也使停机阶段传输更少的页,从而达到同时降低总迁移时间和停机时间的目的。     

一种基于脏页面延迟拷贝的虚拟机动态内存迁移方法

通过对虚拟机动态内存迁移过程中内存页面状态的分析,针对预拷贝算法中脏页面可能被重传这一特点,提出一种基于脏页面预测的迭代传送方法。该方法基于时间局部性原理,在页面迭代传送前对页面未来的变脏程度进行预测,根据预测结果对页面进行状态分类,并对处于不同状态的页面采取相应的传送策略。实验证明,与Xen采取的动态迁移方法相比,提出的方法减少了近10%的迁移总量。     

A data decomposition method for stepwise migration of complex legacy data

Sooner or later, in almost every company, the maintenance and further development of large enterprise information technology (IT) applications reaches its limit. From the point of view of cost as well as technical capability, legacy applications must eventually be replaced by new enterprise IT applications. Data migration is an inevitable part of making this switch. While different data migration strategies can be applied, incremental data migration is one of the most popular strategies, due to its low level of risk: the entire data volume is split into several data tranches, which are then migrated in individual migration steps. The key to a successful migration is the strategy for decomposing the data into suitable tranches. This paper presents a method for data decomposition where the entire data volume of a monolithic enterprise IT application is split into independent data migration tranches. Each tranche comprises the data to be migrated in one migration step, which is usually executed during the application's downtime window. Unlike other methods, which describe data migration in a highly abstract way, we propose specific heuristics for data decomposition into independent data packages (tranches). The data migration approach described here is being applied in one of the largest migration projects currently underway in the European health care sector, comprising millions of customer records.     

存储系统数据迁移技术与实现

通过对存储系统数据迁移常用技术的分析,结合云铜数据迁移实际案例,综合阐述了存储系统数据迁移的技术实现、迁移策略、风险分析与规避、数据完整性与一致性验证方法,对类似系统架构的存储数据迁移具有良好的借鉴意义。     

An adaptive plan-oriented and continuous software migration to cloud in dynamic enterprises

Replacing existing software/hardware components with their equivalent cloud services is an important decision faced by IT managers in today's enterprises. A variety of possible migration targets and cloud services with too many configurations and cost models, disparate and changing strategic objectives of the enterprise management that triggers the migration process, and the complex structure of the legacy applications make software migration to the cloud a challenging issue. In contrast to the existing approaches that model the migration process as an optimization problem to find the optimal deployment of software components on cloud services without presenting a practical migration plan, in this paper, a plan-oriented migration approach is proposed by which the enterprise management is able to follow migration steps of a valid plan. All valid plans are modeled using a labeled transition system, and a recommender engine directs the management through the possible migration paths using predefined fitness functions. It was observed that, particularly in dynamic and changing conditions that a flexible migration plan is essential, the proposed plan-oriented method is very much effective in satisfying the enterprise strategic objectives. Evaluations have been performed using two quality indicators: total cost of ownership and scalability index.     

面向多租户的关键虚拟机动态迁移方法研究

提出一种面向多租户的关键虚拟机动态迁移方法。首先,根据租户对虚拟机的安全需求设定关键虚拟机的比例,减少虚拟机动态迁移的数量;然后,通过虚拟机之间共存时间约束条件最大化降低虚拟机动态迁移的频率;最后,以最小化迁移开销作为虚拟机迁移的目标函数,进一步降低虚拟机迁移带来的开销。实验表明,与现有的防御方法相比,该方法在有效防御侧信道攻击的前提下,能够减少对网络服务性能的影响,降低虚拟机迁移的成本,更加适用于大规模的网络场景。     

基于高可用性的动态漂移技术研究

本文分析了用以提高服务可用性的动态漂移技术的各种实现方法，包括DNS轮转、HTTP报文重定向、IP报文重定向、IP欺骗以及新近提出的连接迁移技术，并着重对连接迁移技术的运行机理进行了深入阐述。文章最后从性能方面对以上方法作了比较。     

Inferring patterns of internal migration from mobile phone call records: evidence from Rwanda

Understanding the causes and effects of internal migration is critical to the effective design and implementation of policies that promote human development. However, a major impediment to deepening this understanding is the lack of reliable data on the movement of individuals within a country. Government censuses and household surveys, from which most migration statistics are derived, are difficult to coordinate and costly to implement, and typically do not capture the patterns of temporary and circular migration that are prevalent in developing economies. In this paper, we describe how new information and communications technologies (ICTs), and mobile phones in particular, can provide a new source of data on internal migration. As these technologies quickly proliferate throughout the developing world, billions of individuals are now carrying devices from which it is possible to reconstruct detailed trajectories through time and space. Using Rwanda as a case study, we demonstrate how such data can be used in practice. We develop and formalize the concept of inferred mobility, and compute this and other metrics on a large data set containing the phone records of 1.5 million Rwandans over four years. Our empirical results corroborate the findings of a recent government survey that notes relatively low levels of permanent migration in Rwanda. However, our analysis reveals more subtle patterns that were not detected in the government survey. Namely, we observe high levels of temporary and circular migration, and note significant heterogeneity in mobility within the Rwandan population. Our goals in this research are thus twofold. First, we intend to provide a new quantitative perspective on certain patterns of internal migration in Rwanda that are unobservable using standard survey techniques. Second, we seek to contribute to the broader literature by illustrating how new forms of ICT can be used to better understand the behavior of individuals in developing countries.     

基于模糊满意度的软件定义网络交换机迁移策略

针对软件定义网络中多控制器间负载均衡的迁移代价和迁移效率问题,提出一种基于模糊满意度的交换机迁移策略。首先,构建均衡判断矩阵,监测控制器负载状态,且提出交换机组选择度,划分交换机组以选取迁移交换机;其次,考虑迁移代价和负载均衡率,构建模糊满意度迁移竞争模型,且提出改进蚁群算法优化求解,选择最佳迁入控制器;最后,将迁移交换机迁往迁入控制器,实现交换机的快速迁移。实验结果表明,与现有交换机迁移策略相比,所提方法在保证较高负载均衡率的同时,进一步优化了网络性能,迁移代价平均减少约26.8%,控制器平均响应时间缩短约0.41 s,改善了交换机迁移过程。     

支持EJB动态分布的组件迁移模型与算法

Web应用服务器是Web计算环境下的新型中间件,为基于组件的分布式Web应用提供了基础运行平台.组件静态分布限制了事务性Web应用在运行期间适应执行环境变化的能力.为了满足Web应用的动态分布需求,Web应用服务器需在底层为组件提供一种动态迁移的能力.如何维持组件迁移前后的一致性是组件迁移中最棘手的问题之一.为解决此问题,定义了组件迁移一致性约束CMC(component migration constrains),并给出了在J2EE(Java 2 platform enterpnse edition)应用服务器中支持EJB(enterprise Java Bean)动态分布的组件迁移模型和SLB Copy,SFB_Copy,EB_Copy 3个迁移算法.分析得出SLB_Copy,SFB_Copy和EB_Copy均满足CMC约束.迁移模型和算法已在自主研制的Web应用服务器WebFrame2.0中实现,并已应用到自适应负载平衡、失效恢复等多个方面.     

虚拟机快速全系统在线迁移

虚拟机全系统在线迁移对于广域网或者没有共享存储的局域网中的虚拟化平台非常重要.然而,全系统映像一般在几十吉字节(gigabyte,GB)量级,迁移这些数据需占用大量I/O带宽且时间开销很大.快速全系统在线迁移方法具有如下特点:文件系统感知的磁盘同步,利用文件系统的磁盘块分配位图,只拷贝实际使用的磁盘块,显著减少了第1阶段同步的磁盘映像数据量;异或压缩,利用映像数据的自相似性,快速有效地减少了迁移最后两个阶段拷贝的数据量;流水迁移,流水化迁移各个阶段,使得读写映像、压缩解压映像、网络收发各阶段充分并行.实验表明,与传统压缩迁移相比,快速迁移可以减少50%的迁移时间,最好情况和平均情况下,能分别降低21.68%和14.48%的停机时间.在网络带宽受限或虚拟机负载过重等极限条件下,快速迁移同样有效.     

MOSIX进程迁移机制研究

MOSIX是一个优秀的集群系统软件，它对Linux内核进行了扩充，采用自适应资源管理方法，通过抢占式进程迁移实现动态负载平衡。该文简要介绍了进程迁移及MOSIX系统，主要分析了MOSIX进程迁移的实现机制。