HDFS-1362 requires DataNode to reload configuration file during the runtime, so that DN can change the data volumes dynamically. This JIRA reuses the reconfiguration framework introduced by HADOOP-7001 to enable DN to reconfigure at runtime.
Dynamically add new volumes to DataStorage, formatted if necessary.
Make FSDataset support adding data volumes dynamically
Make FsDataset and DataStore support removing volumes.
Add command line option to ask DataNode reload configuration.
Avoid calling checkDisk when an HDFS volume is removed during a write.