Hadoop DFS (cont)
Datanodes ...
- provide file read/write/append operations to clients
- under instruction from Namenode
- periodically send reports to Namenode
A Hadoop file
- is a collection of fixed-size blocks
- blocks are distributed/replicated across nodes
Datanode → Namenode reports
- Heartbeat ... Datanode still functioning ok
- Blockreport ... list of all blocks on DataNode
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