DataNode is a software node running on a separate machine in an HDFS instance; usually a Hadoop cluster contains a NameNode and a large number of DataNodes. DataNodes are usually organized in the form of racks, and all racks connect all systems through a switch. stand up.
The operating environment of this article: Windows 10 system, nodejs version 12.19.0, Dell G3 computer.
What does datanode mean?
DataNode is a software node running on a separate machine in an HDFS instance. Usually a Hadoop cluster contains a NameNode and a large number of DataNodes. DataNodes are usually organized in the form of racks, and all racks connect all systems through a switch.
DataNodes respond to read and write requests from HDFS clients. They also respond to commands to create, delete and copy blocks from the NameNode. The NameNode relies on periodic heartbeat messages from each DataNode. Each message contains a block report against which the NameNode can verify block mappings and other file system metadata. If the DataNode cannot send heartbeat messages, the NameNode will take repair measures. Re-replicate the missing blocks on this node.
Datenode provides storage services for real file data.
File block (block): the most basic storage unit. For the file content, the length of a file is size, then starting from the 0 offset of the file, the files are divided and numbered in a fixed size order, and each divided one is called a Block. HDFS default BIock size is 128MB.
Different from ordinary file systems, in HDFS, if a file is smaller than the size of a data block, it does not occupy the entire data storage space.
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