BREAKDOWN OF HDFS-6581 SUBTASKS AND RELATED JIRAS HDFS-6921. Add LazyPersist flag to FileStatus. (Arpit Agarwal) HDFS-6924. Add new RAM_DISK storage type. (Arpit Agarwal) HDFS-6922. Add LazyPersist flag to INodeFile, save it in FsImage and edit logs. (Arpit Agarwal) HDFS-6923. Propagate LazyPersist flag to DNs via DataTransferProtocol. (Arpit Agarwal) HDFS-6925. DataNode should attempt to place replicas on transient storage first if lazyPersist flag is received. (Arpit Agarwal) HDFS-6926. DN support for saving replicas to persistent storage and evicting in-memory replicas. (Arpit Agarwal) HDFS-6927. Initial unit tests for lazy persist files. (Arpit Agarwal) HDFS-6929. NN periodically unlinks lazy persist files with missing replicas from namespace. (Arpit Agarwal) HDFS-6928. 'hdfs put' command should accept lazyPersist flag for testing. (Arpit Agarwal) HDFS-6960. Bugfix in LazyWriter, fix test case and some refactoring. (Arpit Agarwal) HDFS-6931. Move lazily persisted replicas to finalized directory on DN startup. (Arpit Agarwal) HDFS-6950. Add Additional unit tests for HDFS-6581. (Xiaoyu Yao via Arpit Agarwal)