jps

hadoop namenode -format

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dfs directory : /home/hadoop/dfs

• 　　--data
  • 　　--current/VERSION

  •               #Wed Jul 
                  
                    30
                  
                  
                    20
                  
                  :
                  
                    41
                  
                  :
                  
                    03
                  
                   CST 
                  
                    2014
                  
                  
                    
    
    storageID
                  
                  =DS-ab96ad90-
                  
                    7352
                  
                  -4cd5-a0de-
                  
                    7308c8a358ff
    
    
                    
                      
                        clusterID
                      
                    
                  
                  
                    
                      =CID-aa2d4761-974b-
                      
                        4451
                      
                      -
                      
                        8858
                      
                      -
                    
                  
                  
                    
                      
                        bbbcf82e1fd4
                      
                    
                    
    
    cTime
                  
                  =
                  
                    0
                  
                  
                    
    
    datanodeUuid
                  
                  =a3356a09-780c-43e8-a721-
                  
                    45aecf9bdb96
    
    storageType
                  
                  =
                  
                    DATA_NODE
    
    layoutVersion
                  
                  =-
                  
                    55
                  
                

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• 　　--name
  • 　　 --/current/VERSION

  •               #Wed Jul 
                  
                    30
                  
                  
                    20
                  
                  :
                  
                    39
                  
                  :
                  
                    00
                  
                   CST 
                  
                    2014
                  
                  
                    
    
    namespaceID
                  
                  =
                  
                    895092439
                  
                  
                    
                      
                         clusterID
                      
                      =CID-aa2d4761-974b-
                      
                        4451
                      
                      -
                      
                        8858
                      
                      -
                    
                  
                  
                    
                      
                        bbbcf82e1fd4
                      
                    
                    
    
    cTime
                  
                  =
                  
                    0
                  
                  
                    
    
    storageType
                  
                  =
                  
                    NAME_NODE
    
    blockpoolID
                  
                  =BP-
                  
                    152997847
                  
                  -
                  
                    127.0
                  
                  .
                  
                    0.1
                  
                  -
                  
                    1406723940846
                  
                  
                    
    
    layoutVersion
                  
                  =-
                  
                    56
                  
                

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•           
              
                Block Pool
              
              
                A Block Pool is a set of blocks that belong to a single namespace.
              
              
  
              Datanodes store blocks 
            
            
              for
            
             all the block pools 
            
              in
            
             the cluster. 
            
  
            It is managed independently of other block pools. 
            
  
            This allows a namespace to generate Block IDs 
            
              for
            
             new blocks without the need 
            
              for
            
             coordination with the other namespaces. 
            
  
            The failure of a Namenode does not prevent the datanode from serving other Namenodes 
            
              in
            
            
               the cluster.
  
  
  
  A 
              
                Namespace
              
               and its 
              
                block pool
              
               together are called 
              
                Namespace Volume
              
              . 
              
  
              It is a self
            
            -contained unit of management. When a Namenode/
            
              namespace is deleted, 
              
  
              the corresponding block pool at the datanodes is deleted. Each namespace volume is upgraded as a unit, during cluster upgrade.
  
  
  
  
              
                ClusterID
              
              
  
  
  
  A new identifier ClusterID is added to 
              
                identify all the nodes 
              
            
            
              
                in
              
               the cluster
            
            . When a Namenode is formatted, 
            
  
            this identifier is provided or auto generated. 
            
              This ID should be used 
              
                for
              
               formatting the other Namenodes into the cluster.
            
          

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hadoop namenode多次格式化后，導致datanode啟動不了