LayerMover: Fast virtual machine migration over WAN with three-layer image structure

Live Virtual Machine (VM) migration across data centers is an important technology to facilitate cloud management and deepen the cooperation between cloud providers. Without the support of a shared storage system between data centers, migrating the storage data (i.e. virtual disk) of a VM becomes the bottleneck of live VM migration over Wide Area Network (WAN) due to the contradiction between the low bandwidth of the Internet and the comparatively large size of VM storage data. According to previous studies, many inter- and intra-VM duplicated blocks exist between VM disk images. Therefore, data deduplication is widely used for accelerating VM storage data migration. However, it must make a trade-off between computation cost and transmission benefit. Existing approaches are fragile as they explore only the static data feature of image files without much consideration on data semantics. They may adversely influence on migration performance when the benefit resulting from data deduplication cannot remedy its computation overhead. In this paper, we propose a new space-efficient VM image structure-three-layer structure. According to different functions and features, the data of a VM are separated into an Operating System (OS) layer, a Working Environment (WE) layer, and a User Data (UD) layer. Based on this structure, we design a novel VM migration system-LayerMover. It mainly focuses on improving migration performance through optimizing the data deduplication technique. Our experimental results show that three-layer image structure can improve data sharing between VMs, and the similarity ratio between WE images can reach 70%. The tests for LayerMover indicate that it can be significantly beneficial to VM migration across data centers, especially when multiple VMs which share base images are migrated.