Cloud computing is a novel paradigm capable of rationalizing the use of computational resources by means of outsourcing and virtualization. Elasticity is one of the most attractive features of cloud computing. Elastic clouds are able to adapt to workload changes by provisioning and de-provisioning resources in an autonomic manner, such that at each point in time the available resources match the current demand as closely as possible. However, elasticity adds complexity, which makes quantitative analysis of cloud performance and power consumption difficult. Such analysis is required to evaluate and quantify the cost-benefit of a strategy portfolio and the quantitative runtime performance and power consumption experienced by cloud-users. In this study, we present a comprehensive analytical approach to performance and power consumption analysis of elastic clouds. Several metrics are defined and evaluated: expected task completion time, power consumption rate, and task rejection rate under different load conditions, elasticity intensities, and error intensities. To validate the proposed approach, we obtain experimental data through a real-world cloud and conduct a confidence interval analysis. The analysis results suggest the perfect coverage of theoretical results by corresponding experimental confidence intervals. 4368 K.-Y. GUO ET AL.up/out as long as the workload is high, and scaling back in/down when possible, which potentially brings energy saving and operational cost reduction. Elasticity is one of the essential characteristics of scalable cloud, which distinguish the cloud paradigm from traditional computing systems such as gird and cluster computing. However, elasticity is not always welcomed because it also leads to nonnegligible performance degradations caused by lack of available computing resources when facing bursty/high workload and extra operational cost needed by up-scaling/down-scaling activities.Another notable feature influencing performance and power consumption of elastic cloud is machine error. Such errors are caused by accidental storage unavailability, component malfunction, software bug, software aging, storage space fragmentation accumulation, memory leak, extra-longresponse message, connection failure, message loss, wrong input sequence, external intrusion, and so on. Errors are a major reason causing performance and availability degradation in cloud computing systems. Such degradation could be further amplified because of the fact that elastic cloud usually maintains a subset of active machines rather than put all machines online. Such reduced number of active machines are obviously more susceptible to machine errors than those of non-elastic clouds where all machines are kept active.Errors occur at different levels, and not all errors especially hardware and platform-related errors can be detected and repaired by operating system-level (OS-level) detectors. The complexity of error hierarchy and the fact that lower-level hardware/platform errors are more rare than higherlevel software/tas...