MCQs on HDFS Data Integrity and Fault Tolerance | Hadoop HDFS

This set of 30 multiple-choice questions covers key concepts of HDFS data integrity and fault tolerance mechanisms. Topics include block replication, data node failure, heartbeats, block reports, and managing under-replication.

Topic 1: Block Replication Mechanism

1. What is the default replication factor for blocks in HDFS?
   a) 1
   b) 2
   c) 3
   d) 4
2. What does the replication factor of a block in HDFS ensure?
   a) Fast data access
   b) High availability and fault tolerance
   c) Data encryption
   d) Data compression
3. In HDFS, what happens if a block’s replication count falls below the replication factor?
   a) The block is deleted
   b) The block is replicated to meet the replication factor
   c) The block is marked as corrupted
   d) No action is taken
4. What is the primary benefit of block replication in HDFS?
   a) Improved disk space usage
   b) Enhanced data consistency
   c) Fault tolerance and data availability
   d) Faster block retrieval
5. Which of the following is true about block replication in HDFS?
   a) The replication factor can only be set during block creation
   b) Replication happens asynchronously in the background
   c) HDFS does not allow any replication changes after block creation
   d) Replication increases the disk space usage by 100%
6. How does HDFS ensure that data is replicated across different DataNodes?
   a) Using round-robin scheduling
   b) Using a master node to assign blocks to DataNodes
   c) Randomly assigning blocks to nodes
   d) Replication is done based on proximity
7. What happens if a DataNode becomes unavailable in HDFS?
   a) The data is automatically deleted
   b) The block is replicated from other DataNodes
   c) HDFS stops processing data until the node is restored
   d) The data becomes read-only
8. How can the replication factor for a specific file be changed in HDFS?
   a) By modifying the file’s metadata
   b) By editing the file contents
   c) By using the hdfs dfs -setrep command
   d) Replication factor cannot be changed after file creation
9. Which process in HDFS is responsible for handling block replication?
   a) Namenode
   b) DataNode
   c) ResourceManager
   d) JobTracker
10. When does HDFS automatically replicate a block to other DataNodes?
    a) When a file is first created
    b) When a block’s replica is lost
    c) When a DataNode is overloaded
    d) When the system detects a slow disk

Topic 2: Data Node Failure and Recovery

11. What happens to data when a DataNode fails in HDFS?
    a) The data is permanently lost
    b) The system continues to work but with decreased performance
    c) Data is automatically recovered from other replicas
    d) A manual recovery process is required
12. How does HDFS handle the failure of a DataNode?
    a) It moves all blocks to a different node
    b) It starts replicating lost blocks to healthy nodes
    c) It deletes the failed DataNode’s data
    d) It automatically assigns new blocks to the failed node
13. How does HDFS ensure fault tolerance in the event of multiple DataNode failures?
    a) By increasing the replication factor automatically
    b) By relying on the redundancy of the Namenode
    c) By using a master backup node
    d) By maintaining multiple replicas across different nodes
14. In HDFS, what happens if there is no replica of a block after a DataNode failure?
    a) The block is considered lost
    b) HDFS will stop the job
    c) A new replica of the block is created
    d) The system triggers manual intervention
15. Which of the following is true about DataNode failure in HDFS?
    a) The block is automatically deleted
    b) The replication factor of the block is reduced
    c) HDFS waits until the DataNode comes back online
    d) HDFS attempts to replicate the data to healthy nodes
16. What mechanism does HDFS use to recover from a DataNode failure?
    a) HDFS automatically triggers block replication
    b) It uses a secondary DataNode to recover the data
    c) The Namenode is responsible for replicating data
    d) A third-party tool is required for recovery
17. What is the impact of a DataNode failure on a file’s availability in HDFS?
    a) The file becomes unavailable until recovery
    b) The file is deleted automatically
    c) The file is still available if replicas are intact
    d) A file’s data cannot be recovered if a DataNode fails
18. Which component detects DataNode failures in HDFS?
    a) ResourceManager
    b) Namenode
    c) JobTracker
    d) DataNode itself
19. How are DataNode failures reported in HDFS?
    a) By alerting the user through the UI
    b) By sending a heartbeat signal to the Namenode
    c) By broadcasting a failure message
    d) By updating the block report
20. How does the Namenode respond when it detects a DataNode failure?
    a) It triggers block replication to other available DataNodes
    b) It reassigns the failed DataNode’s blocks to other nodes
    c) It sends a recovery command to the DataNode
    d) It halts all data processing until recovery

Topic 3: Heartbeats and Block Reports

21. What is the purpose of heartbeats in HDFS?
    a) To monitor system load
    b) To detect and manage DataNode failures
    c) To synchronize file replicas
    d) To manage block replication
22. What happens if a DataNode stops sending heartbeats to the Namenode?
    a) The DataNode is assumed to be failed
    b) The Namenode triggers a block replication immediately
    c) The DataNode is removed from the cluster
    d) The DataNode is suspended for manual recovery
23. What information is included in a block report sent by a DataNode?
    a) The list of files being processed
    b) The health status of the DataNode
    c) The list of all blocks on the DataNode
    d) The number of replicas for each block
24. How frequently are heartbeats sent from a DataNode to the Namenode in HDFS?
    a) Every 10 seconds
    b) Every minute
    c) Every 3 seconds
    d) Every 30 seconds
25. How does the Namenode use block reports to maintain HDFS integrity?
    a) By tracking block locations and ensuring replication consistency
    b) By deleting blocks that are not needed anymore
    c) By compressing blocks to optimize storage
    d) By monitoring the status of each DataNode’s disk usage
26. What happens if a DataNode fails to send a block report?
    a) The blocks are assumed to be lost
    b) The DataNode is marked as dead after a certain timeout
    c) The report is automatically retried
    d) Block replication is halted until the report is received
27. How can an administrator manually trigger a block report in HDFS?
    a) By restarting the DataNode
    b) By using the hdfs dfs -report command
    c) By sending a heartbeat to the Namenode
    d) Block reports are triggered automatically, no manual action required
28. Which of the following is a consequence of missing or delayed heartbeats from a DataNode?
    a) File corruption
    b) Block under-replication
    c) DataNode reboots
    d) Faster data processing
29. What triggers the Namenode to consider a DataNode as failed in HDFS?
    a) Failure to send heartbeats for a specific time
    b) DataNode exceeding its storage limit
    c) DataNode becoming overloaded
    d) DataNode receiving too many block reports
30. What happens if the block report indicates a block is missing in HDFS?
    a) The block is replicated from other available DataNodes
    b) The block is deleted from the system
    c) The block is flagged as corrupted
    d) A manual recovery process is initiated

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