HDFS-7254. Add documentation for hot swaping DataNode drives (Lei Xu via Colin P. McCabe)

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -284,6 +284,9 @@ Release 2.7.0 - UNRELEASED
 
     HDFS-7221. TestDNFencingWithReplication fails consistently. (Charles Lamb via wang)
 
+    HDFS-7254. Add documentation for hot swaping DataNode drives (Lei Xu via
+    Colin P. McCabe)
+
   OPTIMIZATIONS
 
   BUG FIXES

hadoop-hdfs-project/hadoop-hdfs/src/site/apt/HDFSCommands.apt.vm

@@ -194,6 +194,7 @@ HDFS Commands Guide
           [-refreshSuperUserGroupsConfiguration]
           [-refreshCallQueue]
           [-refresh <host:ipc_port> <key> [arg1..argn]]
+          [-reconfig <datanode|...> <host:ipc_port> <start|status>]
           [-printTopology]
           [-refreshNamenodes datanodehost:port]
           [-deleteBlockPool datanode-host:port blockpoolId [force]]
@@ -287,6 +288,12 @@ HDFS Commands Guide
                   | of the resource specified by \<key\> on \<host:ipc_port\>.
                   | All other args after are sent to the host.
 *-----------------+-----------------------------------------------------------+
+| -reconfig <datanode|...> <host:ipc_port> <start|status> | Start
+                  | reconfiguration or get the status of an ongoing
+                  | reconfiguration. The second parameter specifies the node
+                  | type. Currently, only reloading DataNode's configuration is
+                  | supported.
+*-----------------+-----------------------------------------------------------+
 | -printTopology  | Print a tree of the racks and their nodes as reported by
                   | the Namenode
 *-----------------+-----------------------------------------------------------+

hadoop-hdfs-project/hadoop-hdfs/src/site/apt/HdfsUserGuide.apt.vm

@@ -486,6 +486,26 @@ HDFS Users Guide
     This is because data inconsistency can result if an edit log operation
     refers to the destination of an automatically renamed file.
 
+* DataNode Hot Swap Drive
+
+   Datanode supports hot swappable drives. The user can add or replace HDFS data
+   volumes without shutting down the DataNode. The following briefly describes
+   the typical hot swapping drive procedure:
+
+     * If there are new storage directories, the user should format them and mount them
+       appropriately.
+
+     * The user updates the DataNode configuration <<<dfs.datanode.data.dir>>>
+       to reflect the data volume directories that will be actively in use.
+
+     * The user runs <<<dfsadmin -reconfig datanode HOST:PORT start>>> to start
+       the reconfiguration process. The user can use <<<dfsadmin -reconfig
+       datanode HOST:PORT status>>> to query the running status of the reconfiguration
+       task.
+
+     * Once the reconfiguration task has completed, the user can safely <<<umount>>>
+       the removed data volume directories and physically remove the disks.
+
 * File Permissions and Security
 
    The file permissions are designed to be similar to file permissions on