What is NameNode ha?
The HDFS NameNode High Availability feature enables you to run redundant NameNodes in the same cluster in an Active/Passive configuration with a hot standby. In the case of an unplanned event such as a machine crash, the cluster would be unavailable until an operator restarted the NameNode. …
What is ha in Hadoop?
The high availability feature in Hadoop ensures the availability of the Hadoop cluster without any downtime, even in unfavorable conditions like NameNode failure, DataNode failure, machine crash, etc. It means if the machine crashes, data will be accessible from another path.
How does Hadoop HA work?
Hadoop HDFS provides High availability of data. When the client requests NameNode for data access, then the NameNode searches for all the nodes in which that data is available. After that, it provides access to that data to the user from the node in which data was quickly available.
How do I manually start NameNode?
By following methods we can restart the NameNode:
- You can stop the NameNode individually using /sbin/hadoop-daemon.sh stop namenode command. Then start the NameNode using /sbin/hadoop-daemon.sh start namenode.
- Use /sbin/stop-all.sh and the use /sbin/start-all.sh, command which will stop all the demons first.
How do I know if Namenode is active?
- List the namenode hostnames. # hdfs getconf -namenodes. c2301-node2.coelab.cloudera.com c2301-node3.coelab.cloudera.com.
- Get nameservice name. # hdfs getconf -confKey dfs.nameservices. nameservice1.
- Get active and standby namenodes. # hdfs getconf -confKey dfs.ha.namenodes.nameservice1. namenode11,namenode20. # su – hdfs.
What is high availability cloudera?
In Cloudera Manager, HA is implemented using Quorum-based storage. Enabling HA enables automatic failover as part of the same command. Cluster Administrator (also provided by Full Administrator) The Enable High Availability workflow leads you through adding a second (standby) NameNode and configuring JournalNodes.
What is standby NameNode in Hadoop?
At any point in time, exactly one of the NameNodes is in an Active state, and the others are in a Standby state. The Active NameNode is responsible for all client operations in the cluster, while the Standby is simply acting as a slave, maintaining enough state to provide a fast failover if necessary.
How do I know if NameNode is active?
How do I access Namenode in Hadoop?
The default address of namenode web UI is http://localhost:50070/ . You can open this address in your browser and check the namenode information. The default address of namenode server is hdfs://localhost:8020/ . You can connect to it to access HDFS by HDFS api.
How do I run Namenode in Hadoop?
Run the command % $HADOOP_INSTALL/hadoop/bin/start-dfs.sh on the node you want the Namenode to run on. This will bring up HDFS with the Namenode running on the machine you ran the command on and Datanodes on the machines listed in the slaves file mentioned above.
How do you get NameNode?
To find the active namenode, we can try executing the test hdfs command on each of the namenodes and find the active name node corresponding to the successful run. Below command executes successfully if the name node is active and fails if it is a standby node.
What is the role of NameNode in HDFS?
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. When the NameNode goes down, the file system goes offline.
When to use a NameNode in a HA cluster?
This allows a fast failover to a new NameNode in the case that a machine crashes, or a graceful administrator-initiated failover for the purpose of planned maintenance. In a typical HA cluster, two or more separate machines are configured as NameNodes.
How to configure ha namenodes in HDFS site?
To configure HA NameNodes, you must add several configuration options to your hdfs-site.xml configuration file. The order in which you set these configurations is unimportant, but the values you choose for dfs.nameservices and dfs.ha.namenodes. [nameservice ID] will determine the keys of those that follow.
What happens when a Name node fails in Hadoop?
Prior to Hadoop 2.0.0, the NameNode was a single point of failure (SPOF) in an HDFS cluster. Each cluster had a single NameNode, and if that machine or process became unavailable, the cluster as a whole would be unavailable until the NameNode was either restarted or brought up on a separate machine.
What kind of storage do you need for NameNode?
Shared storage – you will need to have a shared directory which the NameNode machines have read/write access to. Typically this is a remote filer which supports NFS and is mounted on each of the NameNode machines. Currently only a single shared edits directory is supported.