Why use an NFS soft mount vs. a hard mount for NameNode storage directories?
Use the Network Files System (NFS) soft mount as the NameNode directory to detect potential NFS directory issues. When using an NFS soft mount, the NameNode will generate errors if there are issues with the mounted directory. In contrast, using a hard mount will not generate an error within the NameNode. This is because using an NFS hard mount will cause the NameNode process to continually wait for a response from the NFS server. Thus, an administrator will not be able to determine if there is an issue with the NameNode.
NOTE: Using a hard mount can cause applications on a linux system to hang, hence NameNode can hang as well. Please do not use hard mounts for Namenode and Datanode data directories.