In Hadoop HDFS Federation the latest step of adding a new NameNode to an existing HDFS cluster is:
==> Refresh the Datanodes to pickup the newly added Namenode by running the following command against all the Datanodes in the cluster:
[hdfs]$ $HADOOP_PREFIX/bin/hdfs dfsadmin -refreshNameNodes <datanode_host_name>:<datanode_rpc_port>
Witch is the best place to execute the flowing command: NameNode or datanode ?
If I have 1000 Datanodes is it logical to run it 1OOO time ?
In namenode run this command once.
$HADOOP_PREFIX/sbin/slaves.sh hdfs dfsadmin -refreshNameNodes <datanode_host_name>:<datanode_rpc_port>
slaves.sh script will distribute the command to all the slave hosts which are mentioned in slaves file (typically placed in $HADOOP_CONF_DIR)
Related
i have created a hadoop cluster and wanted to add a new node node in the cluster running as a slave without restarting the master node
how can this be acheived
Datanodes and nodemanagers can be added without restarting the namenode(s) or resource manager(s).
More specifically, these need to be ran on the machines of those running services
Namenode
hdfs dfsadmin -refreshNodes
ResourceManager
rmadmin -refreshNodes
I have a multi-node standalone hadoop cluster for HDFS. I am able to load data to HDFS, however everytime I reboot my computer and start the cluster by start-dfs.sh, I don't see the dashboard until I perform hdfs namenode -format which erases all my data.
How do I start hadoop cluster without having to go through hdfs namenode -format?
You need to shutdown hdfs and the namenode cleanly (stop-dfs) before you shutdown your computer. Otherwise, you can corrupt the namenode, causing you to need to format to get back to a clean state
I have a cluster of 5 machines:
1 big NameNode
4 standard DataNodes
I want to change my current NameNode with a DataNode without losing the data stored in HDFS, so my cluster could become:
1 standard NameNode
3 standard DataNodes
1 big DataNode
Does someone know a simple way to do that?
Thank you very much
Decomission data node where namenode will be moved.
Stop the cluster.
Create a tar of dfs.name.dir from current namenode.
Copy all hadoop config files from current NN to target NN.
Replace the name/ip of target namenode by modifying core-site.xml.
Restore tarball of dfs.name.dir. Make sure that full path is same.
Now start the cluster by starting new namenode and one less datanode.
Verify that everything is working perfectly.
Add old namenode as datanode by configuring it as datanode.
I would suggest to uninstall and then install hadoop on both the nodes so that previous configuration does not cause any problem.
I am getting java.io.IOException: Failed to load an FSImage file while starting Namenode
ERROR org.apache.hadoop.hdfs.server.namenode.FSImage: Failed to load image from FSImageFile(file=/opt1/dfs/nn/current/fsimage_0000000000023479779, cpktTxId=0000000000023479779)
java.io.IOException: Unexpected block size: -1945969516689645797
java.io.IOException: Failed to load an FSImage file!
And namenode is not getting started because of this.
I have 1 namenode, 1 seconday namenode and 3 datanodes in my cluster.
Can someone help me recover my cluster.
Try formatting the namenode:
hadoop namenode -format
Note that in order to have access permission for formatting you must execute the command as hdfs user.
In order the switch for example from cloudera user to hdfs do the following:
sudo bash
su - hdfs
If you still get errors regarding the datanode I probably need to clear the datanode folder:
Try deleting first the datanode folder (you can find it in the configuration file under dos.data.dir, dfs.datanode.data.dir).
If you have a cloudera-quickstart-vm the location is /var/lib/hadoop-hdfs/cache/hdfs/dfs/data
Stop all data node and secondary name node and format name node using the command:
sudo -u hdfs hdfs namenode -format
Restart name node and data nodes
I am fairly new to hadoop. For running some benchmarks, I need variety of hadoop configuration for comparison.
I want to know a method to remove a hadoop slave from DFS (not running datanode daemon anymore) but not from Mapred (keep running tasktracker), or vice-versa.
AFAIK, there is a single slave file for such hadoop nodes and not separate slave files for DFS and Mapred.
Currently, I am trying to start both DFS and Mapred on the slave node , and then killing datanode on the slave. But it takes a while to put that node in to 'dead nodes' on HDFS GUI. Any parameter can be tuned to make this timeout quicker ?
Thankssss
Try using dfs.hosts and dfs.hosts.exclude in the hdfs-site.xml, mapred.hosts and mapred.hosts.exclude in mapred-site.xml. These are for allowing/excluding hosts to connect to the NameNode and the JobTracker.
Once the list of nodes in the files has been updated appropriately, the NameNode and the JobTracker have to be refreshed using the hadoop dfsadmin -refreshNodes and hadoop mradmin -refreshNodes command respectively.
Instead of using slaves file to start all processes on your cluster, you can start only required daemons on each machine if you have few nodes.