HDFS-8226. Non-HA rollback compatibility broken (Contributed by J.Andreina)

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

@@ -755,6 +755,8 @@ Release 2.7.1 - UNRELEASED
     HDFS-7980. Incremental BlockReport will dramatically slow down namenode
     startup.  (Walter Su via szetszwo)
 
+    HDFS-8226. Non-HA rollback compatibility broken (J.Andreina via vinayakumarb)
+
 Release 2.7.0 - 2015-04-20
 
   INCOMPATIBLE CHANGES

hadoop-hdfs-project/hadoop-hdfs/src/main/bin/start-dfs.sh

@@ -48,13 +48,14 @@ fi
 
 # get arguments
 if [[ $# -ge 1 ]]; then
-  nameStartOpt="$1"
+  startOpt="$1"
   shift
-  case "$nameStartOpt" in
+  case "$startOpt" in
     -upgrade)
+      nameStartOpt="$startOpt"
     ;;
     -rollback)
-      dataStartOpt="$nameStartOpt"
+      dataStartOpt="$startOpt"
     ;;
     *)
       hadoop_exit_with_usage 1

hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HdfsUserGuide.md

@@ -318,6 +318,8 @@ When Hadoop is upgraded on an existing cluster, as with any software upgrade, it
 
     * stop the cluster and distribute earlier version of Hadoop.
 
+    * run the rollback command on the namenode (`bin/hdfs namenode -rollback`).
+
     * start the cluster with rollback option. (`sbin/start-dfs.sh -rollback`).
 
 When upgrading to a new version of HDFS, it is necessary to rename or delete any paths that are reserved in the new version of HDFS. If the NameNode encounters a reserved path during upgrade, it will print an error like the following: