昨天还好好的集群，今天早上来看又挂掉了，还好是家里的测试服务器集群。。。
首先，查看了Namenode的状态，发现两台Namenode只剩下一台了，赶紧到挂了的那台去查看了logs下的日志：
2016-08-09 16:33:51,526 INFO org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager: Waited 6001 ms (timeout=20000 ms) for a response for sendEdits. Succeeded so far: [10.80.248.17:8486] 2016-08-09 16:33:52,169 INFO org.apache.hadoop.hdfs.server.blockmanagement.CacheReplicationMonitor: Rescanning after 30000 milliseconds 2016-08-09 16:33:52,526 INFO org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager: Waited 7002 ms (timeout=20000 ms) for a response for sendEdits. Succeeded so far: [10.80.248.17:8486] 2016-08-09 16:33:53,527 INFO org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager: Waited 8003 ms (timeout=20000 ms) for a response for sendEdits. Succeeded so far: [10.80.248.17:8486] 2016-08-09 16:33:54,529 INFO org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager: Waited 9004 ms (timeout=20000 ms) for a response for sendEdits. Succeeded so far: [10.80.248.17:8486] 2016-08-09 16:33:55,530 INFO org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager: Waited 10006 ms (timeout=20000 ms) for a response for sendEdits. Succeeded so far: [10.80.248.17:8486] 2016-08-09 16:33:56,531 INFO org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager: Waited 11007 ms (timeout=20000 ms) for a response for sendEdits. Succeeded so far: [10.80.248.17:8486] 2016-08-09 16:33:57,533 INFO org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager: Waited 12008 ms (timeout=20000 ms) for a response for sendEdits. Succeeded so far: [10.80.248.17:8486] 2016-08-09 16:33:58,533 INFO org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager: Waited 13009 ms (timeout=20000 ms) for a response for sendEdits. Succeeded so far: [10.80.248.17:8486] 2016-08-09 16:33:59,534 WARN org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager: Waited 14010 ms (timeout=20000 ms) for a response for sendEdits. Succeeded so far: [10.80.248.17:8486] 2016-08-09 16:34:00,536 WARN org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager: Waited 15011 ms (timeout=20000 ms) for a response for sendEdits. Succeeded so far: [10.80.248.17:8486] 2016-08-09 16:34:01,537 WARN org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager: Waited 16013 ms (timeout=20000 ms) for a response for sendEdits. Succeeded so far: [10.80.248.17:8486] 2016-08-09 16:34:02,538 WARN org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager: Waited 17014 ms (timeout=20000 ms) for a response for sendEdits. Succeeded so far: [10.80.248.17:8486] 2016-08-09 16:34:03,540 WARN org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager: Waited 18015 ms (timeout=20000 ms) for a response for sendEdits. Succeeded so far: [10.80.248.17:8486] 2016-08-09 16:34:04,541 WARN org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager: Waited 19016 ms (timeout=20000 ms) for a response for sendEdits. Succeeded so far: [10.80.248.17:8486] 2016-08-09 16:34:05,525 FATAL org.apache.hadoop.hdfs.server.namenode.FSEditLog: Error: flush failed for required journal (JournalAndStream(mgr=QJM to [10.80.248.17:8486, 10.80.248.18:8486, 10.80.248.19:8486], stream=QuorumOutputStream starting at txid 2947)) java.io.IOException: Timed out waiting 20000ms for a quorum of nodes to respond. at org.apache.hadoop.hdfs.qjournal.client.AsyncLoggerSet.waitForWriteQuorum(AsyncLoggerSet.java:137) at org.apache.hadoop.hdfs.qjournal.client.QuorumOutputStream.flushAndSync(QuorumOutputStream.java:107) at org.apache.hadoop.hdfs.server.namenode.EditLogOutputStream.flush(EditLogOutputStream.java:113) at org.apache.hadoop.hdfs.server.namenode.EditLogOutputStream.flush(EditLogOutputStream.java:107) at org.apache.hadoop.hdfs.server.namenode.JournalSet$JournalSetOutputStream$8.apply(JournalSet.java:533) at org.apache.hadoop.hdfs.server.namenode.JournalSet.mapJournalsAndReportErrors(JournalSet.java:393) at org.apache.hadoop.hdfs.server.namenode.JournalSet.access$100(JournalSet.java:57) at org.apache.hadoop.hdfs.server.namenode.JournalSet$JournalSetOutputStream.flush(JournalSet.java:529) at org.apache.hadoop.hdfs.server.namenode.FSEditLog.logSync(FSEditLog.java:639) at org.apache.hadoop.hdfs.server.namenode.FSEditLog.endCurrentLogSegment(FSEditLog.java:1221) at org.apache.hadoop.hdfs.server.namenode.FSEditLog.rollEditLog(FSEditLog.java:1158) at org.apache.hadoop.hdfs.server.namenode.FSImage.rollEditLog(FSImage.java:1238) at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.rollEditLog(FSNamesystem.java:6344) at org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.rollEditLog(NameNodeRpcServer.java:933) at org.apache.hadoop.hdfs.protocolPB.NamenodeProtocolServerSideTranslatorPB.rollEditLog(NamenodeProtocolServerSideTranslatorPB.java:139) at org.apache.hadoop.hdfs.protocol.proto.NamenodeProtocolProtos$NamenodeProtocolService$2.callBlockingMethod(NamenodeProtocolProtos.java:11214) at org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:619) at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:962) at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2039) at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2035) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.Subject.doAs(Subject.java:422) at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1628) at org.apache.hadoop.ipc.Server$Handler.run(Server.java:2033) 2016-08-09 16:34:05,526 WARN org.apache.hadoop.hdfs.qjournal.client.QuorumJournalManager: Aborting QuorumOutputStream starting at txid 2947 2016-08-09 16:34:05,600 INFO org.apache.hadoop.util.ExitUtil: Exiting with status 1 2016-08-09 16:34:05,733 INFO org.apache.hadoop.hdfs.server.namenode.NameNode: SHUTDOWN_MSG: /************************************************************ SHUTDOWN_MSG: Shutting down NameNode at ut07/10.80.248.17 ************************************************************/
以上是hadoop-hadooptest-namenode-ut07.log在Namenode退出时候的关键日志，可以从中发现，Namenode在写Journalnode发生了超时，默认的超时时间为20秒，而在超时发生后，Namenode会触发ExitUtil类的terminate 方法，导致进程的System.exit()
至于为什么好好的集群，会发生写入超时的问题呢，这个问题现在还不太确定，有人说是因为执行了较大文件的HDFS操作，导致Namenode的FULL GC时间较长，所以导致写Journalnode超时。但是我昨天到今天基本上没有去动HDFS，这个根本原因还得再深挖一下。。。
无论如何，先把集群恢复吧，还要用呢。
其实在实际的生产环境中，也很容易发生类似的这种超时情况，所以我们需要把默认的20s超时改成更大的值，比如60s。
我们可以在hadoop/etc/hadoop下的hdfs-site.xml中，加入一组配置:
<property> <name>dfs.qjournal.write-txns.timeout.ms</name> <value>60000</value> </property>
这也是我从别人博客中看到的配置方法，神奇的是，我在hadoop的官网中的关于hdfs-site.xml介绍中，居然找不到关于这个配置的说明。。。
http://hadoop.apache.org/docs/r2.7.2/hadoop-project-dist/hadoop-hdfs/hdfs-default.xml
最后记得重启整个集群，这样配置才能生效。
友情提示：使用了Flume的同学，记得也要重启Flume集群哦~