What is the use of DataNode?
DataNodes store data in a Hadoop cluster and is the name of the daemon that manages the data. File data is replicated on multiple DataNodes for reliability and so that localized computation can be executed near the data. Within a cluster, DataNodes should be uniform.
What Is Isilon Hadoop?
The Dell EMC Isilon scale-out network-attached storage (NAS) platform provides Hadoop clients with direct access to Big Data through a Hadoop File System (HDFS) interface. Powered by the distributed Dell EMC Isilon OneFS operating system, an Isilon cluster delivers a scalable pool of storage with a global namespace.
What is NameNode and DataNode?
The NameNode keeps an image of the entire file system namespace and file Blockmap in memory. The DataNode stores HDFS data in files in its local file system. The DataNode has no knowledge about HDFS files. It stores each block of HDFS data in a separate file in its local file system.
How do you recommission a DataNode?
To decommision a DataNode:
- Create a file named dfs. exclude in the HADOOP_CONF_DIR (default is /etc/hadoop/conf ).
- Add the name of each DataNode host to be decommissioned on individual lines.
- Stop the TaskTracker on the DataNode to be decommissioned.
- Add the following property to hdfs-site. xml on the NameNode host.
What is the job of the NameNode What about the DataNode?
The NameNode is the centerpiece of an HDFS file system. It keeps the directory tree of all files in the file system, and tracks where across the cluster the file data is kept. It does not store the data of these files itself.
What is the advantage of using Impala over hive?
Using Impala and Hive LLAP
| Impala | Hive LLAP |
|---|---|
| Good choice for Business Intelligence tools that allow users to quickly change queries | Good choice for Dashboards that are pre-defined and not customizable by the viewer |
What is a DataNode?
DataNodes are the slave nodes in HDFS. The actual data is stored on DataNodes. A functional filesystem has more than one DataNode, with data replicated across them. Local and remote client applications can talk directly to a DataNode, once the NameNode has provided the location of the data.
How do you decommission a Datanode in Hadoop?
Decommissioning datanodes in Hadoop cluster
- Check NameNode UI for available data nodes and their status. The picture below shows We have three data nodes in the cluster.
- dfs.hosts.exclude property.
- Update dfs.exclude file.
- Run refreshNodes command.
- Check decommissioning status.
- Check Decommissioned status.
What is DFS Datanode data dir?
dfs. datanode. data. dir can be any directory which is available on the datanode. It can be a directory where disk partitions are mounted like ‘/u01/hadoop/data, /u02/hadoop/data’ which is in case if you have multiple disks partitions to be used for hdfs purpose.
What are the two messages that NameNode receives from DataNode in Hadoop?
Namenode periodically receives a heartbeat and a Block report from each Datanode in the cluster. Every Datanode sends heartbeat message after every 3 seconds to Namenode.
What happens failing DataNode?
If a DataNode fails to heartbeat for reasons other than disk failure, it needs to be recommissioned to be added back to the cluster. If a DataNode rejoins the cluster, there is a possibility for surplus replicas of blocks that were on that DataNode.
Should I use Hive or Impala?
Hive is ideal for situations where multiuser support is required and complex queries which has to span multiple databases are frequently performed. Impala is best suited for business interactive workloads where a low latency is required, and queries have to be interactive.