Abstract: File-backed virtual disk storage is one of the most important parts of virtualization. In order to enhance the efficiency of virtual disk I/O，this paper researched the file-backed disk virtualization on Xen，analysed using asynchronous I/O method to improve I/O rate，and compared the pros and cons of using different format of virtual disk files as storage device of virtual machines.

Key words: storage virtualization, virtual disk image, Xen

摘要： 基于文件的虚拟磁盘存储是虚拟机技术实现的重要一环，为了提高虚拟机磁盘读写效率，着重研究了Xen基于文件的磁盘虚拟化，分析利用异步I/O技术提升虚拟机对虚拟磁盘的读写速度，同时阐述了不同格式的虚拟磁盘文件做为虚拟存储设备的优劣。

关键词: 存储虚拟化, 虚拟磁盘镜像, Xen