| Virtual machine (VM) technology has been widely used in data centersand cloud computing because of its benefits in increasing physical resourcesutilization, easy to manage and so on. As one of the most important featuresof VM technologies, live migration of VMs has the capability of migrating arunning VM transparently from one physical machine to another. It has beenwidely used in a single data center or local area network (LAN) for systemmaintenance, flexible resource management, fault tolerance and so on.Recently, research on live wide-area migration of VMs hasaroused widespread concern, as it will meet the needs of many key casescenarios, such as load balancing among multiple data centers, data centerexpansion and disaster recovery.The current generation of live migration technologies is in generalconfined to LAN. Many mature live migration programs,such as VMwareVMotion and Citrix XenMotion, are based on a shared storage (SAN or NFS)to achieve the sharing of virtual machine disk image. Thus,memory status of VM is the main part of data needs to be transferred from source host to thetarget host in the process of live migration. Pre-copy is the most popularapproach of memory migration. The data transfer rate of live VM migration,which depends on the network condition and data transfer mechanism of livemigration, will have a great impact on the total migration time andon the total amount of migration data, thereby influencing the performanceof live migration.Based on above analysis, this thesis first analyzes the data transfermechanism of live migration by using VMware VMotion and CitrixXenMotion as representatives from the aspect of communications protocol. Itis found that existing live migration technologies mainly adopt one or twoTCP flows to transfer data and their interaction at application layer is quiterare.Then, the thesis sets up test bed to test the data transfer performance oflive migration. The test results show that the data transfer rate andperformance of live migration degrade dramatically with the increase oflatency, even when bandwidth is sufficient. As latency increases with theincrease of transmission distance, live wide-area migration needs to overcomethe impacts of long latency on its data transfer rate so that it can guarantee theperformance of live migration. At last, this thesis designs and implements a live migration accelerationsystem, called LMAS. It uses a pair of transparent proxy servers to acceleratedata transfer of live migration. This means that the acceleration system isindependent on hypervisors. The tunnel of LMAS is divided into two parts,namely, control channel and data channel. Data channel uses parallel TCP asdata transfer mechanism. The test results show that LMAS supports longdistance live migration over1Gbps and10Gbps link. The prototype worksvery well for VMware VMotion and Citrix XenMotion without anymodifications to the hypervisors. In addition, the feature of encrypting dataprovided by LMAS ensures live migration to meet security requirementswhen transferring VMs. |
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