The HDFS system for Hadoop

First, Namenode maintains 2 sheets:

1. File system directory structure, and meta-data information

2. Correspondence between the file and the data block list

stored in the Fsimage and loaded into memory at run time.

Operation Log written to edits

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Second, DataNode

Storage using block form. In Hadoop2, the default size is 128MB.

The security of data is saved using a copy, which is the default number of 3.

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Using the shell to access HDFs

Bin/hdfs dfs–xxx

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Third, RPC (Remote procedure Call)

A remote procedure call needs to have a server (the external exposure method is used by the caller), and a client (the active calling method).

The HDFS system for Hadoop