HDFS架构详解

NameNode（master） and DataNodes（slave  ）

master/slave  的架构

NN: 

　　file system namespace

　　regulates access to files by clients

DN:

　　storage 

HDFS exposes a file system namespace and allows user data to be stored in files

a file is split into one or more blocks and these blocks are stored in a set of DataNodes

　　file size:200M  block size:128M 拆成两个block    容错

 The NameNode executes file system namespace operations like opening, closing, and renaming files and directories

　　CRUD

determines the mapping of blocks to DataNodes