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What is FsImage and EditLog in Hadoop?

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What is FsImage and EditLog in Hadoop?

The FsImage and the EditLog are central data structures of HDFS. A corruption of these files can cause the HDFS instance to be non-functional. For this reason, the NameNode can be configured to support maintaining multiple copies of the FsImage and EditLog.

What is a FsImage in Hadoop?

FsImage is a file stored on the OS filesystem that contains the complete directory structure (namespace) of the HDFS with details about the location of the data on the Data Blocks and which blocks are stored on which node. This file is used by the NameNode when it is started.

What is a namespace in Hadoop?

In Hadoop we refer to a Namespace as a file or directory which is handled by the Name Node. Namespace act as a container where file name grouping and metadata which also contains things like the owners of files, permission bits, block location, size etc will be present.

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What is metadata in Hadoop?

Metadata is the data about the data. Metadata is stored in namenode where it stores data about the data present in datanode like location about the data and their replicas.

What is a metadata namespace?

The Metadata namespace provides classes and methods for working with custom metadata in Salesforce. Salesforce uses metadata types and components to represent org configuration and customization.

What represents the metadata of the namespace?

Essentially, Namespace means a container. In this context it means the file name grouping or hierarchy structure. Metadata contains things like the owners of files, permission bits, block location, size etc.

Where is Fsimage stored?

The FSImage files can be found on the active and standby NameNode, in the NameNode directory which is typically /data/dfs/nn but you can check for the location as per the screenshot below: In the NameNode directory there will be a directory /current: Copies of both the fsimage*_ and the fsimage*.

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Who maintains metadata in Hadoop?

DataNode
Each DataNode keeps a small amount of metadata allowing it to identify the cluster it participates in. If this metadata is lost, then the DataNode cannot participate in an HDFS instance and the data blocks it stores cannot be reached.

How do I read Fsimage?

How to read fsimage:

  1. Donwload the fsimage: hdfs dfsadmin –fetchImage /fsimage.
  2. Reading fsimage:
  3. To get the output on web:
  4. To get the output in to an output directory: hdfs ovi –p Delimited –i /fsimage/fsimage__0000000000000005792 –o /fsimage/fsimage.txt.