MapReduce is an important programming model for processing and generating large data sets in parallel. It is commonly applied in applications such as web indexing, data mining, machine learning, etc. As an open-source implementation of MapReduce, Hadoop is now widely used in industry. Virtualization, which is easy to configure and economical to use, shows great potential for cloud computing. With the increasing core number in a CPU and involving of virtualization technique, one physical machine can hosts more and more virtual machines, but I/O devices normally do not increase so rapidly. As MapReduce system is often used to running I/O intensive applications, decreasing of data redundancy and load unbalance, which increase I/O interference in virtual cloud, come to be serious problems. This paper builds a model and defines metrics to analyze the data allocation problem in virtual environment theoretically. And we design a location-aware file block allocation strategy that retains compatibility with the native Hadoop. Our model simulation and experiment in real system shows our new strategy can achieve better data redundancy and load balance to reduce I/O interference. Execution time of applications such as RandomWriter, Text Sort and Word Count are reduced by up to 33% and 10% on average.