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From Steve Kuo <kuosen...@gmail.com>
Subject Best way to reduce a 8-node cluster in half and get hdfs to come out of safe mode
Date Fri, 06 Aug 2010 05:42:33 GMT
As part of our experimentation, the plan is to pull 4 slave nodes out of a
8-slave/1-master cluster.  With replication factor set to 3, I thought
losing half of the cluster may be too much for hdfs to recover.  Thus I
copied out all relevant data from hdfs to local disk and reconfigure the
cluster.

The 4 slave nodes started okay but hdfs never left safe mode.  The nn.log
has the following line.  What is the best way to deal with this?  Shall I
restart the cluster with 8-node and then delete
/data/hadoop-hadoop/mapred/system?  Or shall I reformat hdfs?

Thanks.

2010-08-05 22:28:12,921 INFO
org.apache.hadoop.hdfs.server.namenode.FSNamesystem.audit:
ugi=hadoop,hadoop       ip=/10.128.135.100      cmd=listStatus
src=/data/hadoop-hadoop/mapred/system   dst=null        perm=null
2010-08-05 22:28:12,923 INFO org.apache.hadoop.ipc.Server: IPC Server
handler 0 on 9000, call delete(/data/hadoop-hadoop/mapred/system, true) from
10.128.135.100:52368: error:
org.apache.hadoop.hdfs.server.namenode.SafeModeException: Cannot delete
/data/hadoop-hadoop/mapred/system. Name node is in safe mode.
The reported blocks 64 needs additional 3 blocks to reach the threshold
0.9990 of total blocks 68. Safe mode will be turned off automatically.
org.apache.hadoop.hdfs.server.namenode.SafeModeException: Cannot delete
/data/hadoop-hadoop/mapred/system. Name node is in safe mode.
The reported blocks 64 needs additional 3 blocks to reach the threshold
0.9990 of total blocks 68. Safe mode will be turned off automatically.
        at
org.apache.hadoop.hdfs.server.namenode.FSNamesystem.deleteInternal(FSNamesystem.java:1741)
        at
org.apache.hadoop.hdfs.server.namenode.FSNamesystem.delete(FSNamesystem.java:1721)
        at
org.apache.hadoop.hdfs.server.namenode.NameNode.delete(NameNode.java:565)
        at sun.reflect.GeneratedMethodAccessor13.invoke(Unknown Source)
        at
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:512)
        at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:968)
        at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:964)
        at java.security.AccessController.doPrivileged(Native Method)
        at javax.security.auth.Subject.doAs(Subject.java:396)
        at org.apache.hadoop.ipc.Server$Handler.run(Server.java:962)

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