The idea here is make it obvious that the admin of a production system is doing something very, very dangerous.

Please mark it as a blocker for 0.19 if required

Re-opening, seems like an easy, valuable improvement.

Provided the simple patch.
Verified the patch manually. Below are the warn logs.

2011-11-06 09:38:31,611 WARN namenode.FSNamesystem (FSNamesystem.java:loadFromDisk(314)) - Only one directory configured for dfs.namenode.name.dir, chances for namespace corruption
2011-11-06 09:38:31,612 WARN namenode.FSNamesystem (FSNamesystem.java:loadFromDisk(319)) - Only one directory configured for dfs.namenode.edits.dir, chances for edits corruption

Not provided the tests because these are just log additions. I feel, not required to start NN for asserting logs.

-1 overall. Here are the results of testing the latest attachment
http://issues.apache.org/jira/secure/attachment/12502638/HDFS-208.patch
against trunk revision .

+1 @author. The patch does not contain any @author tags.

-1 tests included. The patch doesn't appear to include any new or modified tests.
Please justify why no new tests are needed for this patch.
Also please list what manual steps were performed to verify this patch.

+1 javadoc. The javadoc tool did not generate any warning messages.

+1 javac. The applied patch does not increase the total number of javac compiler warnings.

+1 findbugs. The patch does not introduce any new Findbugs (version 1.3.9) warnings.

+1 release audit. The applied patch does not increase the total number of release audit warnings.

-1 core tests. The patch failed these unit tests:
org.apache.hadoop.hdfs.TestFileAppend2
org.apache.hadoop.hdfs.TestBalancerBandwidth

+1 contrib tests. The patch passed contrib unit tests.

Test results: https://builds.apache.org/job/PreCommit-HDFS-Build/1538//testReport/
Console output: https://builds.apache.org/job/PreCommit-HDFS-Build/1538//console

This message is automatically generated.

Test failures are unrelated to this patch!

+1 looks good

Minor update that's a little more explicit (warns of data loss vs nn corruption).

Integrated in Hadoop-Hdfs-trunk-Commit #1363 (See https://builds.apache.org/job/Hadoop-Hdfs-trunk-Commit/1363/)
HDFS-208. name node should warn if only one dir is listed in dfs.name.dir. Contributed by Uma Maheswara Rao G

eli : http://svn.apache.org/viewcvs.cgi/?root=Apache-SVN&view=rev&rev=1204119
Files :

• /hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
• /hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java

Integrated in Hadoop-Common-trunk-Commit #1289 (See https://builds.apache.org/job/Hadoop-Common-trunk-Commit/1289/)
HDFS-208. name node should warn if only one dir is listed in dfs.name.dir. Contributed by Uma Maheswara Rao G

eli : http://svn.apache.org/viewcvs.cgi/?root=Apache-SVN&view=rev&rev=1204119
Files :

• /hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
• /hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java

-1 overall. Here are the results of testing the latest attachment
http://issues.apache.org/jira/secure/attachment/12504409/hdfs-208.patch
against trunk revision .

+1 @author. The patch does not contain any @author tags.

-1 tests included. The patch doesn't appear to include any new or modified tests.
Please justify why no new tests are needed for this patch.
Also please list what manual steps were performed to verify this patch.

-1 patch. The patch command could not apply the patch.

Console output: https://builds.apache.org/job/PreCommit-HDFS-Build/1586//console

This message is automatically generated.

I committed this. Thanks Uma!

Integrated in Hadoop-Mapreduce-trunk-Commit #1315 (See https://builds.apache.org/job/Hadoop-Mapreduce-trunk-Commit/1315/)
HDFS-208. name node should warn if only one dir is listed in dfs.name.dir. Contributed by Uma Maheswara Rao G

eli : http://svn.apache.org/viewcvs.cgi/?root=Apache-SVN&view=rev&rev=1204119
Files :

• /hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
• /hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java

Integrated in Hadoop-Hdfs-trunk #869 (See https://builds.apache.org/job/Hadoop-Hdfs-trunk/869/)
HDFS-208. name node should warn if only one dir is listed in dfs.name.dir. Contributed by Uma Maheswara Rao G

eli : http://svn.apache.org/viewcvs.cgi/?root=Apache-SVN&view=rev&rev=1204119
Files :

• /hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
• /hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java

Integrated in Hadoop-Mapreduce-trunk #903 (See https://builds.apache.org/job/Hadoop-Mapreduce-trunk/903/)
HDFS-208. name node should warn if only one dir is listed in dfs.name.dir. Contributed by Uma Maheswara Rao G

eli : http://svn.apache.org/viewcvs.cgi/?root=Apache-SVN&view=rev&rev=1204119
Files :

• /hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
• /hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java

Integrated in Hadoop-Mapreduce-0.23-Commit #666 (See https://builds.apache.org/job/Hadoop-Mapreduce-0.23-Commit/666/)
HDFS-208. Merge r1204119 from trunk to 0.23 (Revision 1298231)

Result = SUCCESS
suresh : http://svn.apache.org/viewcvs.cgi/?root=Apache-SVN&view=rev&rev=1298231
Files :

• /hadoop/common/branches/branch-0.23/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
• /hadoop/common/branches/branch-0.23/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java

Integrated in Hadoop-Hdfs-trunk-Commit #1926 (See https://builds.apache.org/job/Hadoop-Hdfs-trunk-Commit/1926/)
Moving HDFS-3036, HDFS-3014, HDFS-3003, HDFS-2878, HDFS-208, HDFS-2764, HDFS-2410, HDFS-2285, HDFS-2507 to 0.23.3 section (Revision 1298274)

Result = SUCCESS
suresh : http://svn.apache.org/viewcvs.cgi/?root=Apache-SVN&view=rev&rev=1298274
Files :

• /hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

Integrated in Hadoop-Mapreduce-trunk-Commit #1860 (See https://builds.apache.org/job/Hadoop-Mapreduce-trunk-Commit/1860/)
Moving HDFS-3036, HDFS-3014, HDFS-3003, HDFS-2878, HDFS-208, HDFS-2764, HDFS-2410, HDFS-2285, HDFS-2507 to 0.23.3 section (Revision 1298274)

Result = ABORTED
suresh : http://svn.apache.org/viewcvs.cgi/?root=Apache-SVN&view=rev&rev=1298274
Files :

• /hadoop/common/trunk/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt