以Copy-on-Write架構提昇虛擬機器儲存資料即時遷移之效能

Abstract

To build clusters or data centers with virtual machines, it is required to accompany with an efficient management system. In the virtual machines management system, virtual machine migration could be the most critical challenge for the system administrator. When the environment changes, live migration from the serving machine to another transparently is preferable. In the computing environment combining of cloud computing and virtualization technologies, we can simply connect two different private clouds by live storage migration if both have VMM (virtual machine monitor) supports. Although several VMMs have been presented to support storage migration recently, how to effectively reduce long service downtime and migration time remains a challenging research subject. In this paper, based on kernel-based virtual machines (KVMs), we use the Copy-on-Write (CoW) technology to copy virtual machine file-systems into templates and to record the file-system updates in overlay files. While doing storage migration, we can reduce the transfer time by only sending the overlay files to the destination host if the same template already exists. Most overlay files are transferred using secure remote copy (SCP). That is to say, all on-going updates are iteratively bundled and processed through SCP until the last portion of update, which is transferred using regular QEMU block transformation. Through modification to the source code of QEMU, we are able to effectively accomplish the migration. With applying CoW technology for migration, we can send the template to the destination host in batch. In our experiments, about 80 seconds can be saved without sending a 3GB template file. However, if the virtual machine is running a process with a large number of I/Os, the advantage of using CoW technology will be insignificant.