Cloud computing becomes a well-adopted computing paradigm. With the unprecedented scalability and flexibility, the computational cloud is able to carry out large scale computing tasks in the parallel fashion. The datacenter cloud is a new cloud computing model that use multi-datacenter architectures for large scale massive data processing or computing. In datacenter cloud computing, the overall efficiency of the cloud depends largely on the workload scheduler, which allocates clients' tasks to different Cloud datacenters. Developing high performance workload scheduling techniques in Cloud computing imposes a great challenge which has been extensively studied. Most previous works aim only at minimizing the completion time of all tasks. However, timeliness is not the only concern, while reliability and security are also very important. In this work, a comprehensive Quality of Service (QoS) model is proposed to measure the overall performance of datacenter clouds. An advanced Cross-Entropy based stochastic scheduling (CESS) algorithm is developed to optimize the accumulative QoS and sojourn time of all tasks. Experimental results show that our algorithm improves accumulative QoS and sojourn time by up to 56.1% and 25.4% compared to the baseline algorithm, respectively. The runtime of our algorithm grows only linearly with the number of Cloud datacenters and tasks. Given the same arrival rate and service rate ratio, our algorithm steadily generates scheduling solutions with satisfactory QoS without sacrificing sojourn time. Index Terms-Cloud Computing, DataCenter Clouds, Quality of Service, Workload Scheduling ! 1 INTRODUCTION C LOUD computing [1], which delivers computing as a service, has emerged as a well-adopted computing paradigm which offers vast computing power and flexibility, and an increasing number of commercial cloud computing services are deployed into the market such as Amazon EC2 [2], Google Compute Engine [3], and Rackspace Cloud [4]. The new computing paradigms of "Cloud of Clouds" [5] and "datacenter clouds" [6], [7] are a creation of federated Cloud computing environment that coordinates distributed datacenter computing and achieves high QoS for Cloud applications. Large-scale data-intensive applications across distributed modern datacenter infrastructures is a good implementation and use case of the "Cloud of Clouds" paradigm. A good example for data-intensive analysis is the field of High Energy Physics (HEP). The four main detectors including ALICE, ATLAS, CMS and LHCb at the Large Hadron Collider (LHC) produced about 13 petabyes of data in 2010 [8]. This huge amount of data are stored on the Worldwide LHC Computing Grid that consists of more