server检查的时候。发现存在HDFS上的文件无法同步，再发现hadoop停掉了。
进行重新启动，重新启动不成功。
查看hadoop日志：
2014-07-30 14:15:42,025 INFO org.apache.hadoop.hdfs.server.namenode.FSNamesystem: Roll Edit Log from 192.168.206.133 <span style="color:#ff0000;">2014-07-30 14:15:42,026 WARN org.apache.hadoop.hdfs.server.namenode.FSNamesystem: Cannot roll edit log, edits.new files already exists in all healthy directories: /home/hadoop/hdfs/name/current/edits.new</span> <span style="color:#ff0000;">2014-07-30 14:17:17,853 ERROR org.apache.hadoop.hdfs.server.namenode.FSNamesystem: Unable to sync edit log. java.io.IOException: No space left on device</span> at sun.nio.ch.FileChannelImpl.force0(Native Method) at sun.nio.ch.FileChannelImpl.force(FileChannelImpl.java:348) at org.apache.hadoop.hdfs.server.namenode.FSEditLog$EditLogFileOutputStream.flushAndSync(FSEditLog.java:215) at org.apache.hadoop.hdfs.server.namenode.EditLogOutputStream.flush(EditLogOutputStream.java:89) at org.apache.hadoop.hdfs.server.namenode.FSEditLog.logSync(FSEditLog.java:1017) at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.startFile(FSNamesystem.java:1190) at org.apache.hadoop.hdfs.server.namenode.NameNode.create(NameNode.java:628) at sun.reflect.GeneratedMethodAccessor300.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:563) at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1388) at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1384) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.Subject.doAs(Subject.java:396) at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1121) at org.apache.hadoop.ipc.Server$Handler.run(Server.java:1382) 2014-07-30 14:17:17,853 FATAL org.apache.hadoop.hdfs.server.namenode.FSNamesystem: No edit streams are accessible java.lang.Exception: No edit streams are accessible at org.apache.hadoop.hdfs.server.namenode.FSEditLog.fatalExit(FSEditLog.java:388) at org.apache.hadoop.hdfs.server.namenode.FSEditLog.exitIfNoStreams(FSEditLog.java:407) at org.apache.hadoop.hdfs.server.namenode.FSEditLog.removeEditsAndStorageDir(FSEditLog.java:432) at org.apache.hadoop.hdfs.server.namenode.FSEditLog.removeEditsStreamsAndStorageDirs(FSEditLog.java:470) at org.apache.hadoop.hdfs.server.namenode.FSEditLog.logSync(FSEditLog.java:1030) at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.startFile(FSNamesystem.java:1190) at org.apache.hadoop.hdfs.server.namenode.NameNode.create(NameNode.java:628) at sun.reflect.GeneratedMethodAccessor300.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$Server.call(RPC.java:563) at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1388) at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1384) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.Subject.doAs(Subject.java:396) at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1121) at org.apache.hadoop.ipc.Server$Handler.run(Server.java:1382)
空间满了。
使用命令df -h查看当中一个datanode，果然
但使用du -s查看，但显示仅仅使用几百G，并没有满
这个实候确实让人费解，仅仅好重新启动datanode所在的server。并又一次挂载。回复原样，容量显示正常。
可是这个时候hadoop集群依旧无法重新启动，一直报错：
014-07-30 16:27:46,610 ERROR org.apache.hadoop.hdfs.server.namenode.FSNamesystem: FSNamesystem initialization failed. java.io.IOException: Incorrect data format. logVersion is -32 but writables.length is 0. at org.apache.hadoop.hdfs.server.namenode.FSEditLog.loadFSEdits(FSEditLog.java:560) at org.apache.hadoop.hdfs.server.namenode.FSImage.loadFSEdits(FSImage.java:1026) at org.apache.hadoop.hdfs.server.namenode.FSImage.loadFSImage(FSImage.java:839) at org.apache.hadoop.hdfs.server.namenode.FSImage.recoverTransitionRead(FSImage.java:377) at org.apache.hadoop.hdfs.server.namenode.FSDirectory.loadFSImage(FSDirectory.java:100) at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.initialize(FSNamesystem.java:388) at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.<init>(FSNamesystem.java:362) at org.apache.hadoop.hdfs.server.namenode.NameNode.initialize(NameNode.java:276) at org.apache.hadoop.hdfs.server.namenode.NameNode.<init>(NameNode.java:496) at org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:1279) at org.apache.hadoop.hdfs.server.namenode.NameNode.main(NameNode.java:1288) 2014-07-30 16:27:46,612 ERROR org.apache.hadoop.hdfs.server.namenode.NameNode: java.io.IOException: Incorrect data format. logVersion is -32 but writables.length is 0. at org.apache.hadoop.hdfs.server.namenode.FSEditLog.loadFSEdits(FSEditLog.java:560) at org.apache.hadoop.hdfs.server.namenode.FSImage.loadFSEdits(FSImage.java:1026) at org.apache.hadoop.hdfs.server.namenode.FSImage.loadFSImage(FSImage.java:839) at org.apache.hadoop.hdfs.server.namenode.FSImage.recoverTransitionRead(FSImage.java:377) at org.apache.hadoop.hdfs.server.namenode.FSDirectory.loadFSImage(FSDirectory.java:100) at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.initialize(FSNamesystem.java:388) at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.<init>(FSNamesystem.java:362) at org.apache.hadoop.hdfs.server.namenode.NameNode.initialize(NameNode.java:276) at org.apache.hadoop.hdfs.server.namenode.NameNode.<init>(NameNode.java:496) at org.apache.hadoop.hdfs.server.namenode.NameNode.createNameNode(NameNode.java:1279) at org.apache.hadoop.hdfs.server.namenode.NameNode.main(NameNode.java:1288)
不得解。仅仅好从secondrynamenode尝试恢复
1. 先备份namenode和secondrynamenode的数据
2. 运行checkpoint数据：hadoop namenode –importCheckpoint
失败……
最后查了网上的方法(有一个是改动代码并又一次编译的。就算了)：
printf "\xff\xff\xff\xee\xff" > edits
重新启动失败。继续：
printf "\xff\xff\xff\xee\xff" > edits.new
重新启动成功。
可是问题来了，数据丢失，由于清空了edits文件最新的日志内容。
一般来说，到这份上是没有办法了。
可是，幸好我们有两地同步和备份，将别一个数据中心HDFS集群的数据同步过来。恢复成功。
假设没有异地备份的话，上面的操作我也会慎之又慎的。
