Defects per Million (DPM) Evaluation for a Cloud Dealing with VM Failures Using Checkpointing

In cloud computing systems, a user request goes through several cloud service provider specific processing steps from the instant it is submitted until the service is completed. In this paper, we use service-oriented metrics to characterize the dependability of cloud computing systems in order to find the pitfalls and improve the service. We find that it is not possible to fully reflect the impact of a cloud-service´s dependability behavior through traditional dependability metrics like availability or reliability. We use a user-perceived dependability metric called Defects Per Million (DPM), defined as the number of user requests dropped out of a million. We demonstrate a new formulation for computing DPM metric in cloud computing systems. We incorporate check pointing scheme for job execution in the cloud to mitigate the impact of virtual machine failures, and compute DPM in order to characterize the improvement in the DPM due to the check pointing scheme compared to no-check pointing scheme.