Understanding HDFS cluster FSImage image and looking its contents

FSImage in HDFS Cluster:

  • The HDFS namespace is stored by the NameNode.
  • The entire file system namespace, including the mapping of blocks to files and file system properties, is stored in a file called the FsImage.
  • The FsImage is stored as a file in the NameNode’s local file system too.
  • The NameNode keeps an image of the entire file system namespace and file Blockmap in memory.
  • Reads at startup only and keeps it during the life of start
    • RAM Dependency
    • What about “One Large File” or  “1,000,000 small files”

Step 1: First save the fsimage to local file system (Note: You cannot save the fsimage to HDFS.)

Step 2: Converting saved image to human readable file using –oiv option

Step 3: Now you can open the file in your favorite editor or you can try $head or $tail quickly to peek into.



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