What is the duty of DataNodes in HDFS?
DataNodes sends information to the NameNode about the files and blocks stored in that node and responds to the NameNode for all filesystem operations. 6. When a DataNode starts up it announce itself to the NameNode along with the list of blocks it is responsible for.
Which of the following is a duty of the Namenodes in HDFS?
The correct answer is option A (Manage file system namespace). NameNode acts as a master in Hadoop cluster and assign the tasks to DataNode.
What is the responsibility of secondary name node?
The main function of the Secondary namenode is to store the latest copy of the FsImage and the Edits Log files. How does it help? When the namenode is restarted , the latest copies of the Edits Log files are applied to the FsImage file in order to keep the HDFS metadata latest.
What is role of NameNode and DataNode in Hadoop?
NameNode and DataNodes HDFS exposes a file system namespace and allows user data to be stored in files. Internally, a file is split into one or more blocks and these blocks are stored in a set of DataNodes. The NameNode executes file system namespace operations like opening, closing, and renaming files and directories.
What is the role of NameNode?
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.
How many Namenodes are there in HDFS?
You can have only a single name node in a cluster. Detail – In Yarn / Hadoop 2.0 they have come with a concept of active name node and standby name node. ( This is where most of the people get confused. They consider them to be 2 nodes in a cluster).
How many Namenodes are in HDFS?
What is NameNode and DataNode in big data?
The main difference between NameNode and DataNode in Hadoop is that the NameNode is the master node in Hadoop Distributed File System (HDFS) that manages the file system metadata while the DataNode is a slave node in Hadoop distributed file system that stores the actual data as instructed by the NameNode.
What is Fsimage and EditLog?
FSimage is a point-in-time snapshot of HDFS’s namespace. Edit log records every changes from the last snapshot. The last snapshot is actually stored in FSImage.
What is the difference between a NameNode and a secondary NameNode?
Secondary namenode is just a helper for Namenode. It gets the edit logs from the namenode in regular intervals and applies to fsimage. Once it has new fsimage, it copies back to namenode. Namenode will use this fsimage for the next restart, which will reduce the startup time.
What happens if a DataNode fails?
As soon as the datanodes are declared dead. Data blocks on the failed Datanode are replicated on other Datanodes based on the specified replication factor in hdfs-site. xml file. Once the failed datanodes comes back the Name node will manage the replication factor again.
What data is stored in NameNode?
NameNode only stores the metadata of HDFS – the directory tree of all files in the file system, and tracks the files across the cluster. NameNode does not store the actual data or the dataset. The data itself is actually stored in the DataNodes.
How many DataNodes can be run on a single Hadoop?
With 100 DataNodes in a cluster, 64GB of RAM on the NameNode provides plenty of room to grow the cluster.”
How many NameNodes can run on a single Hadoop cluster?
What is the job of the NameNode?
What happens when NameNode fails?
Whenever the active NameNode fails, the passive NameNode or the standby NameNode replaces the active NameNode, to ensure that the Hadoop cluster is never without a NameNode. The passive NameNode takes over the responsibility of the failed NameNode and keep the HDFS up and running.
What if NameNode goes down?
When the NameNode goes down, the file system goes offline. There is an optional SecondaryNameNode that can be hosted on a separate machine. It only creates checkpoints of the namespace by merging the edits file into the fsimage file and does not provide any real redundancy.
Where is FsImage in Hadoop?
FsImage is a file stored on the OS filesystem that contains the complete directory structure (namespace) of the HDFS with details about the location of the data on the Data Blocks and which blocks are stored on which node. This file is used by the NameNode when it is started.
Which of the following commands will give information on the status of DataNodes?
The dfsadmin –report command produces useful output that shows basic statistics of the cluster, including the status of the DataNodes and NameNode, the configured disk capacity and the health of the data blocks.
What if secondary NameNode fails?
If NameNode gets fail the whole Hadoop cluster will not work. Actually, there will not any data loss only the cluster work will be shut down, because NameNode is only the point of contact to all DataNodes and if the NameNode fails all communication will stop.
What is the difference between NameNode and DataNode in Hadoop?
The main difference between NameNode and DataNode in Hadoop is that the NameNode is the master node in Hadoop Distributed File System that manages the file system metadata while the DataNode is a slave node in Hadoop distributed file system that stores the actual data as instructed by the NameNode.
How do you find the number of DataNodes in Hadoop cluster?
- You can run hdfs dfsadmin -report .
- I tried this.
- It gives the number of nodes when you run it with dfs admin privilege.
- It gives me everything including a summary Datanodes available: 8 (8 total, 0 dead) .
What is the difference between single node and multi node?
As the name says, Single Node Hadoop Cluster has only a single machine whereas a Multi-Node Hadoop Cluster will have more than one machine. In a single node hadoop cluster, all the daemons i.e. DataNode, NameNode, TaskTracker and JobTracker run on the same machine/host.