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Where does Name node store fsImage and edit Log?

I am a java programmer, learning Hadoop. I read that the Name node in HDFS stores its information into two files namely fsImage & editLog. In case of start up it reads this data from the disk & performs checkpoint operation.

But at many places I also read that Name Node stores the data in RAM & that is why apache recommends a machine with high RAM for Name Node server.

Please enlighten me on this. What data does it store in RAM & where does it store fsImage and edit Log ?

Sorry if I asked anything obvious.

Solution

  • To answer:

    What data does it store in RAM & where does it store fsImage and edit Log ?

    In RAM — file to block and block to data node mapping. In persistent storage (includes both edit log and fsimage) — file related metadata (permissions, name and so on).

    For more: FolksTalk — NameNode, Secondary NameNode and Safe Mode – Hadoop Tutorial