MCQs on HDFS Data Consistency and Integrity | Hadoop HDFS
Learn HDFS Data Consistency and Integrity to ensure reliable and secure data storage. This chapter focuses on atomicity in file operations, checksum verification, block corruption handling, and snapshot and backup mechanisms in HDFS.
1. Atomicity in HDFS File Operations
- What does atomicity in HDFS file operations guarantee?
- A) File operations can be undone
- B) File operations are always successful
- C) File operations are completed fully or not at all
- D) File operations occur in real-time
- How does HDFS ensure atomicity in file write operations?
- A) By using file versioning
- B) By using replication
- C) By committing operations in full transactions
- D) By locking the files before writing
- What is the primary benefit of atomic operations in HDFS?
- A) Reduced latency
- B) Fault tolerance and data consistency
- C) Enhanced file compression
- D) Increased storage capacity
- Which mechanism in HDFS helps maintain atomicity during file writes?
- A) Write-ahead logs
- B) Transaction logs
- C) Two-phase commit
- D) Block-level replication
- How does HDFS recover from incomplete file writes?
- A) By rolling back the transaction
- B) By deleting the file automatically
- C) By storing backups of files
- D) By relying on replication
- What happens if a DataNode fails during an atomic file operation?
- A) The operation is automatically retried on another DataNode
- B) The file is replicated immediately
- C) The operation is considered unsuccessful and rolled back
- D) The data is moved to a backup storage
2. Checksum Verification and Block Corruption Handling
- What is the purpose of checksum verification in HDFS?
- A) To track file access patterns
- B) To detect and correct block corruption
- C) To improve data storage efficiency
- D) To compress data during storage
- How does HDFS handle corrupted blocks?
- A) The block is immediately deleted
- B) HDFS checksums the block to verify integrity
- C) The block is replicated from other DataNodes
- D) The block is replaced with a backup
- What happens when a corrupted block is detected in HDFS?
- A) HDFS marks the block for deletion
- B) HDFS tries to repair the block automatically
- C) HDFS ignores the block and continues operations
- D) The NameNode notifies the DataNode to fix the block
- What is the default checksum algorithm used by HDFS?
- A) SHA-1
- B) CRC32
- C) MD5
- D) SHA-256
- How are checksum files stored in HDFS?
- A) In the same directory as the data files
- B) In a separate checksum directory
- C) Within the block metadata
- D) They are not stored separately
- What is the impact of corrupted blocks on HDFS operations?
- A) HDFS stops all operations until the block is repaired
- B) Corrupted blocks cause temporary access delays
- C) HDFS continues operations but may lose data integrity
- D) Operations are not affected, but corruption is logged
- Which command checks for checksum integrity in HDFS?
- A)
hdfs fsck - B)
hdfs dfs -checksum - C)
hdfs dfs -verifyChecksum - D)
hdfs checksum -check
- A)
- What happens if a DataNode is unable to correct a corrupted block?
- A) The block is permanently lost
- B) The block is marked for deletion
- C) The block is re-replicated from other DataNodes
- D) The block is stored as-is
3. Data Integrity Issues in HDFS and Solutions
- Which of the following is a common data integrity issue in HDFS?
- A) Data loss due to disk failure
- B) Data corruption during replication
- C) Inconsistent metadata
- D) All of the above
- How does HDFS resolve issues caused by disk failures?
- A) By using replication to ensure data availability
- B) By compressing the data to reduce storage
- C) By increasing the block size
- D) By encrypting the data
- What is the role of the HDFS NameNode in data integrity?
- A) It checks and verifies block checksums
- B) It manages metadata and block locations
- C) It compresses data for storage
- D) It handles the actual data replication
- What happens if HDFS encounters inconsistent metadata?
- A) HDFS reprocesses the data
- B) The system becomes unavailable until the issue is resolved
- C) HDFS automatically fixes the metadata
- D) The NameNode removes the affected files
- How does HDFS handle network partitioning to prevent data integrity issues?
- A) By temporarily disabling write operations
- B) By replicating data across multiple clusters
- C) By requiring manual intervention to resolve partitions
- D) By using the journal-based mechanism for transaction recovery
- What is the solution when HDFS detects inconsistent replication?
- A) HDFS increases the replication factor to restore consistency
- B) The system shuts down until replication is fixed
- C) HDFS initiates a data consistency check across the cluster
- D) HDFS deletes extra copies automatically
- How does HDFS ensure data integrity during network failure?
- A) By storing redundant data on multiple DataNodes
- B) By using stronger checksum algorithms
- C) By rescheduling operations to unaffected DataNodes
- D) By waiting for network recovery before processing further
4. Understanding HDFS Snapshot and Backup Mechanism
- What is the purpose of HDFS snapshots?
- A) To back up the entire HDFS
- B) To create a read-only copy of the filesystem at a given point in time
- C) To track metadata changes over time
- D) To provide a backup for lost data
- How are HDFS snapshots created?
- A) Using the
hdfs snapshot createcommand - B) Automatically by the NameNode every 24 hours
- C) By running a custom backup job
- D) Using the
hdfs snapshot -takecommand
- A) Using the
- How are snapshots useful in maintaining data integrity?
- A) They provide a history of changes for auditing purposes
- B) They create point-in-time copies of the data for recovery
- C) They eliminate the need for regular backups
- D) They prevent data corruption
- Can HDFS snapshots be deleted?
- A) No, they are permanent once created
- B) Yes, but only after 7 days
- C) Yes, using the
hdfs snapshot deletecommand - D) No, they are removed automatically after 30 days
- What is the difference between HDFS snapshots and traditional backups?
- A) Snapshots are real-time, while backups occur periodically
- B) Snapshots consume more storage space than backups
- C) Snapshots are slower to create than backups
- D) There is no difference
- How are HDFS backups typically performed?
- A) By creating snapshots regularly
- B) By exporting data to external storage systems
- C) By replicating data to a backup cluster
- D) By using the
hdfs backupcommand
- What happens if a snapshot becomes corrupted?
- A) The entire HDFS cluster is shut down
- B) The snapshot is deleted automatically
- C) The snapshot can be recovered from a backup
- D) The data in the snapshot is permanently lost
- How does HDFS minimize the impact of taking a snapshot on system performance?
- A) By using copy-on-write techniques
- B) By performing snapshots during off-peak hours
- C) By compressing data before taking snapshots
- D) By running snapshot operations in parallel
- How can you restore data from an HDFS snapshot?
- A) By using the
hdfs snapshot restorecommand - B) By copying data manually from the snapshot directory
- C) By copying the entire snapshot to a new location
- D) By recovering data from the snapshot during a system crash
- A) By using the
Answers
| Qno | Answer |
|---|---|
| 1 | C) File operations are completed fully or not at all |
| 2 | C) By committing operations in full transactions |
| 3 | B) Fault tolerance and data consistency |
| 4 | C) Two-phase commit |
| 5 | A) By rolling back the transaction |
| 6 | C) The operation is considered unsuccessful and rolled back |
| 7 | B) To detect and correct block corruption |
| 8 | C) The block is replicated from other DataNodes |
| 9 | B) HDFS tries to repair the block automatically |
| 10 | B) CRC32 |
| 11 | A) In the same directory as the data files |
| 12 | B) Corrupted blocks cause temporary access delays |
| 13 | A) hdfs fsck |
| 14 | C) The block is re-replicated from other DataNodes |
| 15 | D) All of the above |
| 16 | A) By using replication to ensure data availability |
| 17 | B) It manages metadata and block locations |
| 18 | B) The system becomes unavailable until the issue is resolved |
| 19 | C) By requiring manual intervention to resolve partitions |
| 20 | A) HDFS increases the replication factor to restore consistency |
| 21 | C) By rescheduling operations to unaffected DataNodes |
| 22 | B) To create a read-only copy of the filesystem at a given point in time |
| 23 | A) Using the hdfs snapshot create command |
| 24 | B) They create point-in-time copies of the data for recovery |
| 25 | C) Yes, using the hdfs snapshot delete command |
| 26 | A) Snapshots are real-time, while backups occur periodically |
| 27 | B) By exporting data to external storage systems |
| 28 | C) The snapshot can be recovered from a backup |
| 29 | A) By using copy-on-write techniques |
| 30 | B) By copying data manually from the snapshot directory |