Sage-Tips

What if replication factor is 3 and 2 nodes are available?

If replication factor is 3 (which is default replication factor) But you have only two datanodes then in that case the Data blocks will be replicated to 2 DataNodes and you might see many “Under Replicated Blocks” because there is not 3rd DataNode.

What happens if DataNode fails while writing a file in the HDFS?

I read from hadoop operations that if a datanode fails during writing process, A new replication pipeline containing the remaining datanodes is opened and the write resumes. The namenode will notice that one of the blocks in the file is under-replicated and will arrange for a new replica to be created asynchronously.

What happens if we change the replication factor in HDFS?

2 Answers. But changing the replication factor for a directory will only affect the existing files and the new files under the directory will get created with the default replication factor ( dfs. replication from hdfs-site.

What will happen if any data node fails what will happen if the name node fails in Hadoop 1 and Hadoop 2?

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.

When using HDFS what occurs when a file is deleted from the command line?

Q 20 – When using HDFS, what occurs when a file is deleted from the command line? A – It is permanently deleted if trash is enabled.

What happens if a Datanode fails?

What happens if one of the Datanodes gets failed in HDFS? 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 if Job Tracker fails?

A TaskTracker will notify the JobTracker when a task fails. The JobTracker decides what to do then: it may resubmit the job elsewhere, it may mark that specific record as something to avoid, and it may may even blacklist the TaskTracker as unreliable. When the work is completed, the JobTracker updates its status.

Is there any way to change the replication of files on HDFS after they are already written to HDFS?

Click on the HDFS tab on the left. Click on the config tab. Under “General,” change the value of “Block Replication” Now, restart the HDFS services.

What happens if you increase and decrease the replication factor from previously configured value?

Increasing/Decreasing the replication factor in HDFS has a impact on Hadoop cluster performance. As the replication factor increases, the NameNode needs to store the more metadata about the replicated copies. So it needs a lot experience for the Hadoop administrator to set the replication factor.

How to get the replication factor of an HDFS file?

method 1: You can use the HDFS command line to ls the file. The second column of the output will show the replication factor of the file. The out.txt’s replication factor is 3. method 2: Get the replication factor using the stat hdfs command tool. Using the above file as an example:

Why do we need to have copy of blocks in HDFS?

The default is 3. Interview Q2> Why do we need to have copy of blocks in cluster. HDFS is built on commodity hardware, hence there could be a failure which would result in loss of data. To ensure high data availability blocks are replicated so that if one block is lost data can be fetched from the other.

What is HDFS in Hadoop?

Hadoop Distributed File System i.e. HDFS is used in Hadoop to store the data means all of our data is stored in HDFS. Hadoop is also known for its efficient and reliable storage technique. So have you ever wondered how Hadoop is making its storage so much efficient and reliable?

Why do we need replication in Hadoop?

Making Replicates of this data is quite easy which provides us fault tolerance and high availability in our Hadoop cluster. As the blocks are of a fixed configured size we can easily maintain its record. Replication ensures the availability of the data.