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What are the differences between the 3 concepts: (1) namenode metadata, (2) namenode image, and (3) edit logs?

BTW,I know the secondary namenode backups namenode data.

I was told that there is another daemon which also backups meta data . Is that true? What is the daemon? Thanks.

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  • Boris Shkolnik at Nov 16, 2009 at 10:22 pm
    NameNode metadata - is in memory data structures describing file system
    structure (directories, files, and file's blocks).

    NameNode image is on-disk representation of the metadata. (fsimage file).

    Edit logs - is a journal that keeps all the events that cause changes in the
    metadata and allows restoration in case of NameNode failure.

    Secondary Namenode - runs checkpoints from time to time. During a checkpoint
    edit logs are merged into metadata and saved to fsimage, which is pushed to
    the NameNode.

    Boris.

    On 11/16/09 12:45 PM, "Steve Gao" wrote:

    What are the differences between the 3 concepts: (1) namenode metadata, (2)
    namenode image, and (3) edit logs?

    BTW,I know the secondary namenode backups namenode data.

    I was told that there is another daemon which also backups meta data . Is that
    true? What is the daemon? Thanks.




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postedNov 16, '09 at 8:46p
activeNov 16, '09 at 10:22p
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