Hadoop HDFS Overview
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What is the first step when a client wants to write data in HDFS?

  • The client writes data to data nodes directly.
  • The data nodes acknowledge receipt of the data blocks.
  • The client connects to the Name Node (NN) to write data. (correct)
  • The Name Node (NN) helps the client replicate missing blocks.

    • In the context of HDFS, what is the purpose of the replication factor?

  • To determine how many copies of a block are stored across the nodes. (correct)
  • To optimize read bandwidth for large files.
  • To spread data across different nodes for load balancing.
  • To ensure that all data is written to a single node.

    • What configuration provides the greatest reliability in HDFS replication strategy?

  • All replicas are stored on different racks. (correct)
  • Replicas are evenly distributed across all nodes.
  • All replicas are stored on different nodes in the same rack.
  • All replicas are stored on a single node.

    • Which of the following is a characteristic of the HDFS architecture?

    <p>Offers reliable storage through multiple copies of data blocks.</p> Signup and view all the answers

    What are the possible interfaces for interacting with HDFS?

    <p>Either web-based or command line interface.</p> Signup and view all the answers

    What is one of the primary motivations for using HDFS?

    <p>To store data on multiple machines</p> Signup and view all the answers

    What type of hardware does HDFS primarily utilize?

    <p>Commodity hardware</p> Signup and view all the answers

    How does HDFS address hardware failure?

    <p>By replicating the data across multiple nodes</p> Signup and view all the answers

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

    <p>To control the file system namespace</p> Signup and view all the answers

    What is a characteristic of the rack in an HDFS setup?

    <p>It is a collection of approximately 40-50 DataNodes</p> Signup and view all the answers

    In HDFS, what does the Secondary Name Node primarily serve as?

    <p>Checkpoint node</p> Signup and view all the answers

    Which of the following statements about data replication in HDFS is true?

    <p>At least one replica must always be on a different rack</p> Signup and view all the answers

    What is a critical function of the Data Node in HDFS?

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

    What is the first step in the block replication policy for a replication factor of three?

    <p>Put the first replica on the local rack</p> Signup and view all the answers

    In the described HDFS architecture, which node is primarily responsible for managing the replication of blocks?

    <p>Name Node (NN)</p> Signup and view all the answers

    Where should the second replica be stored in a replication factor of three according to the block replication policy?

    <p>On a different DataNode in the same rack</p> Signup and view all the answers

    What is the purpose of the Secondary Name Node (SNN) in the HDFS architecture?

    <p>To store a backup of the Name Node's data</p> Signup and view all the answers

    What is indicated as a significant risk in the HDFS architecture concerning the Name Node?

    <p>It is a single point of failure.</p> Signup and view all the answers

    How does the HDFS architecture address network performance?

    <p>Through distributed data processing across multiple racks</p> Signup and view all the answers

    In a multiple-rack cluster, what is the strategy for placing the third replica?

    <p>On a different rack entirely</p> Signup and view all the answers

    Which component is responsible for ensuring the reliability of block storage?

    <p>Name Node (NN)</p> Signup and view all the answers

    What element is primarily responsible for maintaining the filesystem's metadata in HDFS?

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

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

    <p>It performs housekeeping and backups of Name Node metadata.</p> Signup and view all the answers

    In HDFS, what happens if the Name Node does not receive a heartbeat from a Data Node for 10 minutes?

    <p>The Name Node starts to replicate the blocks from that Data Node.</p> Signup and view all the answers

    Why does HDFS design the read operation where clients read directly from Data Nodes?

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

    What does the 'edit log' in HDFS do?

    <p>It records changes to the filesystem.</p> Signup and view all the answers

    How does the Name Node decide which replica of a block a client should read in HDFS?

    <p>It chooses the replica based on load balancing.</p> Signup and view all the answers

    What is the function of a 'heartbeat' in HDFS?

    <p>To indicate that a Data Node is alive and functioning.</p> Signup and view all the answers

    What replication factor is associated with File 1 as per the description provided?

    <p>3</p> Signup and view all the answers

    Study Notes

    HDFS Overview

    • HDFS stands for Hadoop Distributed File System

    • Motivations for HDFS:

      • Data too large for single machine storage
      • Expensive high-end machines aren't required. Commodity hardware can be used.
      • Commodity hardware is prone to failure. The software needs to handle such failures.
      • If one machine storing the data fails, the data needs to be replicated.
      • Distributed machines need to coordinate to organize the data

    • HDFS Architecture: Master-Slave

      • Master: Name Node (NN)
        • Controller of the file system
        • Maintains file system name space
        • Manages block mappings
      • Slave: Data Node (DN)
        • Work horses of the system
        • Perform block operations and replication
        • Secondary Name Node (SNN)
          • Checkpoint node for NN

    • Commodity hardware: readily available, inexpensive, and interchangeable. Synonymous with off-the-shelf hardware.

    • Rack awareness policies:

      • Limit replica placement to a single node
      • Limit replicas to two in a rack
      • Common case: replication factor of three.
        • First replica is placed on the local rack.
        • Second replica on a different node within the same rack.
        • Third replica on different racks.

    • HDFS relies on replication for reliability. If a node fails, another node with a copy of the data can be utilized.

    • Rack: Collection of around 40 to 50 DataNodes connected to the same network switch.

    • A large Hadoop cluster is deployed across multiple racks.

    • HDFS Inside: Name Node

      • Snapshot of File System
      • Edit log (records changes to the File System)
      • Files, replication factors, and block IDs are maintained by the Name Node.
      • Periodically, the NN replicates data to the SNN for backup purposes

    • HDFS Inside: Read

      • Client connects to the NN to locate data blocks
      • NN sends location of data blocks to the client
      • Client reads blocks directly from data nodes.
      • Resilient to node failures (client connects to another node)

    • HDFS Inside: Write

      • Client connects to NN to write data
      • NN tells client to write to certain data nodes.
      • Client writes to the data nodes with the desired replication factor.
      • Handles node failures by replicating missing blocks
      • Replication Strategy vs Tradeoffs: Tradeoff example for write bandwidth vs reliability vs read bandwidth.

    • HDFS Interface

      • Web-based, Command-line (Hadoop FS Shell)

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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), including its architecture, motivations, and functionality. Learn about the roles of the Name Node and Data Nodes, as well as the importance of data replication and failure handling in a distributed environment.

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