A Virtual Disk I/O Monitoring Method And Applications Based On Xen

Virtualization is the support technology of cloud computing, and it hailed as a breakthrough in information industry. Hard disk is an essential I/O device in computer servers, providing the basic data read/write service. Because virtual disk has a high performance requirement and its internal states are difficult to control, it becomes a bottleneck that restricts the performance and functionality of a virtual machine. Our research was based on virtualization technology and Xen virtualization platform. The paper analyzed principles and implementations of disk virtualization and focused on Xen virtual disk model. Then we tested three virtual disk formats in Xen platform and four types of reading and writing methods of virtual disk. After that, this paper explored characters and impacts of different virtual disk format and reading and writing types.Xen was lack of real-time monitoring for virtual disk states, and related applications based on the virtual disk also had an urgent need for virtual disk I/O monitoring. Therefore, we designed and implemented a virtual disk I/O monitoring method based on Xen which was named DM (Disk Monitor). After a detailed analysis of device discovery process and I/O transformation process in HVM and PVHVM model, we proved that if selected the correct intercept point and identified the intercepted content, virtual disk I/O can be real-time monitored. In order to ensure reliability, performance, and scalability of the DM, DM’s modules were divided into two parts:kernel modules and user modules. Kernel modules included a monitoring module and a communication module while user modules included a communication module, a data collection module, a virtual disk operating module, and a user interaction module. Through the interaction of these modules, DM completed the basic functions, such as monitor virtual disk states, display the virtual disk I/O, start or pause listener for a specified virtual disk, I/O playback, and I/O blocking. Functional tests and validations in four scenarios suggested that, DM was able to complete requirements of virtual disk I/O monitoring, and was able to provide APIs for operation and management of the virtual disk.In enterprise-class datacenter, virtual machine backup and recovery is a critical function and has a wide range of applications. But Xen only use snapshot to complete VM backup and recovery. Furthermore, virtual disk backup can only be limited to use LVM existing snapshot function. On the basis of DM, this article designed, implemented, and tested DM-based virtual machine backup. Virtual machine backup completed functions below:enhanced snapshot, incremental backup, differential backup and continuous data protection. These functions apply to universal virtual disk devices, and then effectively compensated for the limitations of the original snapshot in Xen. At the same time, based on the block-class data, incremental backup, differential backup and continuous data protection can effectively meet the needs of storage backup and recovery in datacenter. In addition, in a distributed storage environment and WAN environment, with the help of MD (disk migration), the whole-system migration of virtual machines could benefit integration of physical resources and reduce the power consumption. The article further detailed the architectural design of the whole-system migration based on DM.Finally, this paper made a summary of facing problems about disk virtualization, and analyzed of the future research work.