HDFS Daemons
In Hadoop HDFS there are 2 daemons. All the daemons run on their own JVMs in the background to support required services.
1. NameNode
- Namenode daemon runs on all the masters.
- This daemon manages the HDFS filesystem namespace. NameNode stores metadata like file name, path, number of blocks, block Ids, block locations, number of replicas, slave related config etc.Â
- It keeps the record of the changes created in file system namespace.
- NameNode keeps the meta data in memory for fast retrival.
2. DataNode
- DataNode daemon runs on all the slaves.
- The function of DataNode is to store the actual data in the HDFS. It contains the actual data blocks. HDFS cluster usually has more than one DataNodes.
- Data is replicated across the other machines present in the HDFS cluster.
HDFS Daemons