四、NameNode啓動過程詳解

NameNode

• 內存
• 本地磁盤
  • fsimage
  • edits

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第一次啓動HDFS

1. 格式化HDFS，目的就是生成fsimage
2. start NameNode，讀取fsimage文件
3. start DataNode，向NameNode註冊；block report（塊彙報）
4. create dir /user/hw/tmp -> write [edits]
5. put files /user/beifeg/tmp(*-site.xml) -> write [edits]
6. delete file /user/beifeng/tmp/core-site.xml -> write [edits]

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第二次啓動HDFS

1. NameNode
   • read [fsimage]
   • read [edits]
   • gen write fsimage [new]
   • gen edits [null]
2. DataNode
   • 註冊
   • block report
3. create dir /user/beifeng/tmp -> write [edits]
4. put files /user/beifeg/tmp(*-site.xml) -> write [edits]
5. delete file /user/beifeng/tmp/core-site.xml -> write [edits]

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SecondaryNameNode輔助功能講解

• NameNode中的編輯日誌文件太大的話如何處理。須要藉助SecondaryNameNode.
• 按期的合併 fsimage+edits ->new fsimage