MapReduce Service (MRS) is a big data cluster running based on the open source Hadoop ecosystem. It provides the capabilities for storing and analyzing massive sets of data, which satisfies user data storage and processing requirements. For details, see MapReduce Service User Guide.
You can use Hive/Spark (analysis cluster of MRS) to store massive volumes of service data. Hive/Spark data files are stored on HDFS. On DWS, you can connect a DWS cluster to an MRS cluster, read data from HDFS files, and write the data to DWS when the clusters are on the same network.