The enormous growth of digital data, especially the data in unstructured format has brought a tremendous challenge on data analysis as well as the data storage systems which are essentially increasing the cost and performance of the backup systems. The traditional systems do not provide any optimization techniques to keep the duplicated data from being backed up. Deduplication of data has become an essential and financial way of the capacity optimization technique which replaces the redundant data. The following paper reviews the deduplication process, types of deduplication and techniques available for data deduplication. Also, many approaches proposed by various researchers on deduplication in Big data storage systems are studied and compared.