Simple and practical disk performance evaluation method in virtual machine environments

This paper proposes a disk access throughput evaluation method in virtual machine environments where multiple independent virtual machines share a common physical shared disk drive. Disk drive simulation is one candidate to evaluate the total performance of disk throughput by modeling I/O management mechanisms inside virtual machine monitors. However, making such a model might be impossible when the source code of a target virtual machine monitor is not open. Therefore, a simple evaluation method is required. We propose a simple and practical method with an analytical model which has only two types of parameters: sequential access ratio and disk performance profile. These two parameters can be obtained without knowledge about operations inside a virtual machine monitor. The sequential access ratio is defined as the probability whether the next disk access is to the same file or not. It represents virtual machine monitorpsilas I/O scheduling characteristics. The disk performance profile is the relationship between seek distance and throughput, and we assume, in this paper, it is measured in advance. We have developed a calculation method by combining the two parameters above. Then we have compared the estimation throughputs and the measured ones in Xen virtual machine environments with random read accesses. The experimental results show that errors of our method are no more than 10%.