HDFS Overview
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Questions and Answers

What is the primary role of the Name Node in HDFS?

  • To handle client requests for data processing
  • To ensure data replication across nodes
  • To store all the data blocks in the cluster
  • To manage metadata and direct data block locations (correct)

    • What happens when a data node fails during write operations in HDFS?

  • The client is notified to find alternative nodes
  • The missing blocks are identified and replicated by the Name Node (correct)
  • The Name Node allocates storage on a new data node instantly
  • The write operation fails and must be retried

    • What is the Secondary Name Node's main purpose in HDFS?

  • To help manage metadata and periodically merge file system images (correct)
  • To serve as a backup for data storage
  • To operate the web-based interface for Hadoop
  • To directly handle read and write operations from clients

    • In HDFS write operations, where are the replicas typically stored to optimize reliability and bandwidth?

    <p>Replicas distributed across different racks</p> Signup and view all the answers

    What is one of the main trade-offs to consider when determining how to replicate data in HDFS?

    <p>Distributing replicas increases reliability but can affect write bandwidth</p> Signup and view all the answers

    What is the primary role of a Data Node in HDFS?

    <p>Handle block operations and replication</p> Signup and view all the answers

    What is the main function of the Name Node in HDFS?

    <p>Manage block mappings and file metadata</p> Signup and view all the answers

    What is the purpose of the Secondary Name Node in HDFS?

    <p>To act as a checkpoint node for the Name Node</p> Signup and view all the answers

    During an HDFS read operation, which component is primarily responsible for serving the requested data?

    <p>Data Node</p> Signup and view all the answers

    Which statement best describes how HDFS handles data replication?

    <p>No more than one replica is placed on one node</p> Signup and view all the answers

    What potential issue does HDFS overcome by utilizing a Master-Slave architecture?

    <p>Data loss due to hardware failures</p> Signup and view all the answers

    How does HDFS ensure efficient organization of data across distributed nodes?

    <p>By implementing a rack-aware policy</p> Signup and view all the answers

    Which of the following statements is NOT true about HDFS write operations?

    <p>The data blocks are directly written to the Name Node</p> Signup and view all the answers

    Which of the following describes the functionality of the Name Node?

    <p>It manages the metadata and namespace of the file system.</p> Signup and view all the answers

    Why does HDFS allow clients to read blocks directly from Data Nodes instead of going through the Name Node?

    <p>To prevent the Name Node from being a bottleneck.</p> Signup and view all the answers

    How does HDFS determine which replica of a block a client should read?

    <p>The client chooses based on the closest Data Node.</p> Signup and view all the answers

    What mechanism does HDFS use to ensure Data Nodes are operational?

    <p>Heartbeats sent every 3 seconds from Data Nodes to the Name Node.</p> Signup and view all the answers

    What role does the edit log play in HDFS?

    <p>It records changes made to the file system.</p> Signup and view all the answers

    What occurs if the Name Node does not hear from a Data Node within 10 minutes?

    <p>It starts replicating the blocks stored on that Data Node.</p> Signup and view all the answers

    Study Notes

    HDFS Overview

    • HDFS stands for Hadoop Distributed File System

    • Motivation for HDFS comes from the following problems:

      • Data too large for a single machine
      • Expensive high-end machines
      • Commodity hardware failure
      • Data loss if a storing machine fails
      • Distributed machines need a coordinated way to organize data

    • HDFS solves these issues via:

      • Storing data on multiple machines
      • Running on commodity hardware
      • Software handling hardware failure
      • Replicating data

    • Commodity hardware is readily available, inexpensive, and interchangeable

    • HDFS uses a Master-Slave architecture

      • Master node (Name Node) controls file system
        • Manages file system name space
        • Manages block mappings
      • Slave nodes (Data Nodes) are workhorses
        • Perform block operations
        • Handle replication

    • Rack awareness policies are used to improve performance

      • No more than one replica on one node
      • No more than two replicas on the same rack
      • For a replication factor of 3
      • First replica on the local rack, second replica on different node in the same rack, third replica on a different rack

    HDFS Inside

    • Name Node handles snapshots of file system, edit logs, replication factors and block IDs
    • Name Node periodically sends control information to Data Nodes
    • Data Nodes are periodically checked by Name Node -if Name Node does not hear from a Data Node within 10 minutes it starts replicating the associated blocks

    HDFS Inside: Read

    • Clients connect directly to Data Nodes to read data
      • Name Node gives directions on where to find data
    • Clients read data from Data Nodes, bypassing Name Node
    • if Data Nodes fail, client can connect to another Data node to get the missing block

    HDFS Inside: Read-Reasons

    • Prevents Name Node from being a bottleneck
    • Allows HDFS to handle many concurrent clients
    • Spreads data traffic across the cluster

    HDFS Inside: Read-Replica Selection

    • Name Node uses rack awareness to select replicas based on network topology

    HDFS Inside: Write

    • Clients connect to Name Node to write data
    • Name Node directs clients to Data Nodes
    • Clients write blocks to Data Nodes using the desired replication factor
    • Name Node handles replication if a Data Node fails

    HDFS Inside: Write-Replication Strategy

    • Different replication strategies have tradeoffs in reliability, write bandwidth, and read bandwidth
      • Putting all replicas on one node maximizes reliability but hurts write and read bandwidth
      • Putting all replicas on different racks balances these factors
    • HDFS replication strategies:
      • 1 -> same node as client
      • 2 -> different node in same rack
      • 3 -> different node in different rack

    HDFS Interface

    • HDFS has a web based interface : http://ccl.cse.nd.edu/operations/hadoop/
    • Command Line Interface : https://hadoop.apache.org/docs/r2.4.1/hadoop-project-dist/hadoop-common/FileSystemShell.html

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    Related Documents

    HDFS Hadoop Distributed File System Lecture 3 PDF

    Description

    This quiz covers the fundamentals of the Hadoop Distributed File System (HDFS). You will learn about its architecture, benefits, and how it addresses data storage challenges using commodity hardware. Gain insights into the Master-Slave structure, file management, and rack awareness policies.

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