Cloud computing systems continue to grow in their scale and complexity. They are changing dynamically as well due to the addition and removal of system components, changing execution environments, frequent updates and upgrades, online repairs and more. In such large-scale complex and dynamic systems, failures are common. In this paper, we present a failure prediction mechanism exploiting both unsupervised and semi-supervised learning techniques for building dependable cloud computing systems. The unsupervised failure detection method uses an ensemble of Bayesian models. It characterizes normal execution states of the system and detects anomalous behaviors. After the anomalies are verified by system administrators, labeled data are available. Then, we apply supervised learning based on decision tree classier to predict future failure occurrences in the cloud. Experimental results in an institute-wide cloud computing system show that our proposed method can forecast failure dynamics with high accuracy.