HDFS Architecture Questions and Answers

Q: What is the default Hadoop dfs block size ?

The default block sizes are 64 MB/128 MB.HDFS stores files in large blocks to reduce seek overhead and the amount of metadata the NameNode must hold. The default block size was 64 MB in Hadoop 1.x and was raised to 128 MB from Hadoop 2.x onwards; it can be changed with the dfs.blocksize setting.32 MB was never the default, and 256 MB is a common setting chosen by administrators for very large files, not the default. So every other pair is wrong.

Q: Role of "data streamer" in Hadoop Distributed File System (HDFS) is :

The DataStreamer sends a request to the Name Node to get a list of suitable Data Nodes to store replica of first block.When a client writes a file to HDFS, the output stream splits the data into packets and places them on a data queue. The DataStreamer consumes that queue: it asks the NameNode to allocate a new block by choosing suitable DataNodes for the replicas, then streams the packets to the first DataNode in the resulting pipeline, which forwards them to the next.The first option reverses the roles of the two node types. Failures of DataNodes are detected through heartbeats and acknowledgements, not by a streaming service, and the NameNode is not monitored this way.

Q: What is the default replication factor in HDFS for a hadoop cluster having 100 data nodes ?

The default replication factor is 3.HDFS stores each block on three DataNodes by default (the dfs.replication setting is 3). With rack awareness, one replica is placed on the writer's node or rack and the other two on a different rack, so the data survives the loss of a node or a whole rack.The default does not depend on the size of the cluster; a 100-node cluster still uses 3 unless an administrator changes it. 1 would leave no redundancy, and 2 and 4 are possible settings but not the default.

What is the default Hadoop dfs block size ?

A.32 MB/64 MB
B.64 MB/128 MB
C.32 MB/128 MB
D.128 MB/256 MB

Exam Year(s)

MH SET - 2021, SET Exam - 2021,

Answer: B

The default block sizes are 64 MB/128 MB.

HDFS stores files in large blocks to reduce seek overhead and the amount of metadata the NameNode must hold. The default block size was 64 MB in Hadoop 1.x and was raised to 128 MB from Hadoop 2.x onwards; it can be changed with the dfs.blocksize setting.

32 MB was never the default, and 256 MB is a common setting chosen by administrators for very large files, not the default. So every other pair is wrong.

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Role of "data streamer" in Hadoop Distributed File System (HDFS) is :

A.Send a request to the Data Node to send list of Name Node to store replica of first block
B.Send a request to the Name Node to get a list of suitable Data Nodes to store replica of first block
C.Streaming service to indicate failure of Data Nodes
D.Streaming service to indicate failure of Name Nodes

Exam Year(s)

MH SET - 2021, SET Exam - 2021,

Answer: B

The DataStreamer sends a request to the Name Node to get a list of suitable Data Nodes to store replica of first block.

When a client writes a file to HDFS, the output stream splits the data into packets and places them on a data queue. The DataStreamer consumes that queue: it asks the NameNode to allocate a new block by choosing suitable DataNodes for the replicas, then streams the packets to the first DataNode in the resulting pipeline, which forwards them to the next.

The first option reverses the roles of the two node types. Failures of DataNodes are detected through heartbeats and acknowledgements, not by a streaming service, and the NameNode is not monitored this way.

Discuss in Forum

What is the default replication factor in HDFS for a hadoop cluster having 100 data nodes ?

Exam Year(s)

MH SET - 2023, SET Exam - 2023,

Answer: C

The default replication factor is 3.

HDFS stores each block on three DataNodes by default (the dfs.replication setting is 3). With rack awareness, one replica is placed on the writer's node or rack and the other two on a different rack, so the data survives the loss of a node or a whole rack.

The default does not depend on the size of the cluster; a 100-node cluster still uses 3 unless an administrator changes it. 1 would leave no redundancy, and 2 and 4 are possible settings but not the default.

Discuss in Forum

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