服務器檢查的時候，發現存在HDFS上的文件無法同步，再發現hadoop停掉了。進行重啓，重啓不成功。
查看hadoop日誌：
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)空間滿了。
使用命令df -h查看其中一個datanode，果然
但使用du -s查看，但顯示只使用幾百G，並沒有滿
這個實候確實讓人費解，只好重啓datanode所在的服務器，並重新掛載，回覆原樣，容量顯示正常。
但是這個時候hadoop集羣依然無法重啓，一直報錯：
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，只好從secondrynamenode嘗試恢復
1. 先備份namenode和secondrynamenode的數據
2. 執行checkpoint數據：hadoop namenode –importCheckpoint
失敗……
最後查了網上的方法(有一個是修改代碼並重新編譯的，就算了)：
printf "\xff\xff\xff\xee\xff" > edits
重啓失敗，繼續：
printf "\xff\xff\xff\xee\xff" > edits.new
重啓成功。
但是問題來了，數據丟失，因爲清空了edits文件最新的日誌內容。
一般來說，到這份上是沒有辦法了。
但是，幸好我們有兩地同步和備份，將別一個數據中心HDFS集羣的數據同步過來，恢復成功。
如果沒有異地備份的話，上面的操作我也會慎之又慎的。