P2V Migration with Post-Copy Hot Cloning for Service Downtime Reduction

We propose a post-copy hot cloning mechanism to reduce service downtime of physical to virtual (P2V) migration. The conventional P2V migration requires to copy disk images from a physical to a virtual machine with stopping the system to ensure the consistency of the disk images, but it usually takes long time (e.g., several hours) because of slow I/O performance of storage devices. The proposed hot cloning mechanism copies disk images from a physical machine to a virtual machine in the background with running the system on the virtual machine. Since the disk image copy is the bottleneck of P2V migration, this hot cloning mechanism drastically reduces the service downtime. To ensure the consistency of disk images during the hot cloning, the hot cloning mechanism provides a block device of the source physical machine and a disk image (or block device) of the destination virtual machine as one virtualized block device that manages all I/O operations to the virtual machine. In this paper, we implement this post-copy hot cloning mechanism using the Linux Network Block Device (NBD) kernel module to support Linux-based hyper visors such as Xen and Linux KVM. We discuss the service downtime that is reduced by the proposed mechanism, and demonstrate that the implementation performs well in practical environments throughout the performance evaluations on the copy speed, hyper visor load, and system performance on a virtual machine.