HDFS-11188. Change min supported DN and NN versions back to 2.x. Contributed by Andrew Wang.

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java

@@ -290,7 +290,7 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
   public static final String  DFS_NAMENODE_MAX_EXTRA_EDITS_SEGMENTS_RETAINED_KEY = "dfs.namenode.max.extra.edits.segments.retained";
   public static final int     DFS_NAMENODE_MAX_EXTRA_EDITS_SEGMENTS_RETAINED_DEFAULT = 10000; // 10k
   public static final String  DFS_NAMENODE_MIN_SUPPORTED_DATANODE_VERSION_KEY = "dfs.namenode.min.supported.datanode.version";
-  public static final String  DFS_NAMENODE_MIN_SUPPORTED_DATANODE_VERSION_DEFAULT = "3.0.0-alpha1-SNAPSHOT";
+  public static final String  DFS_NAMENODE_MIN_SUPPORTED_DATANODE_VERSION_DEFAULT = "2.1.0-beta";
 
   public static final String  DFS_NAMENODE_EDITS_DIR_MINIMUM_KEY = "dfs.namenode.edits.dir.minimum";
   public static final int     DFS_NAMENODE_EDITS_DIR_MINIMUM_DEFAULT = 1;
@@ -613,7 +613,7 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
   public static final int     DFS_DATANODE_IPC_DEFAULT_PORT = 9867;
   public static final String  DFS_DATANODE_IPC_ADDRESS_DEFAULT = "0.0.0.0:" + DFS_DATANODE_IPC_DEFAULT_PORT;
   public static final String  DFS_DATANODE_MIN_SUPPORTED_NAMENODE_VERSION_KEY = "dfs.datanode.min.supported.namenode.version";
-  public static final String  DFS_DATANODE_MIN_SUPPORTED_NAMENODE_VERSION_DEFAULT = "3.0.0-alpha1-SNAPSHOT";
+  public static final String  DFS_DATANODE_MIN_SUPPORTED_NAMENODE_VERSION_DEFAULT = "2.1.0-beta";
   public static final String  DFS_NAMENODE_INODE_ATTRIBUTES_PROVIDER_KEY = "dfs.namenode.inode.attributes.provider.class";
   public static final String  DFS_DATANODE_BP_READY_TIMEOUT_KEY = "dfs.datanode.bp-ready.timeout";
   public static final long    DFS_DATANODE_BP_READY_TIMEOUT_DEFAULT = 20;