Hadoop HDFS Overview
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Questions and Answers

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. (C)</p> Signup and view all the answers

What are the possible interfaces for interacting with HDFS?

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

What is one of the primary motivations for using HDFS?

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

What type of hardware does HDFS primarily utilize?

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

How does HDFS address hardware failure?

<p>By replicating the data across multiple nodes (C)</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 (B)</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 (D)</p> Signup and view all the answers

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

<p>Checkpoint node (D)</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 (B)</p> Signup and view all the answers

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

<p>Performing block operations and replication (B)</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 (C)</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) (B)</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 (C)</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 (A)</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. (C)</p> Signup and view all the answers

How does the HDFS architecture address network performance?

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

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

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

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

<p>Name Node (C)</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. (A)</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. (A)</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. (B)</p> Signup and view all the answers

What does the 'edit log' in HDFS do?

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

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

<p>3 (A)</p> Signup and view all the answers

Flashcards

HDFS

Hadoop Distributed File System; a system for storing and managing large datasets across multiple machines.

Commodity Hardware

Standard, inexpensive computer hardware easily replaceable.

Name Node (NN)

HDFS master node; controls the file system's namespace and block mappings.

Data Node (DN)

HDFS worker nodes that store and manage blocks of data.

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Master-Slave Architecture

HDFS structure with a master controller (Name Node) and worker nodes (Data Nodes).

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Rack

A group of computers connected together using the same network switch.

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Replication

Creating multiple copies of data across different machines for fault tolerance.

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Secondary Name Node (SNN)

A checkpoint node in HDFS that helps with management and recovery in the master-slave architecture.

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Block Replication Policy

The strategy for creating copies of data blocks across different DataNodes in HDFS. This policy ensures data availability and fault tolerance.

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Single Point of Failure

A situation where the failure of one component (like the Name Node) can cause the entire system to fail.

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DataNode

A worker node in HDFS that stores and manages blocks of data. It is responsible for storing and retrieving data.

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Rack Awareness

The Name Node's ability to understand the physical location of DataNodes within racks. This is important for efficient replication and data placement.

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Network Performance

The speed and efficiency of data transfer between nodes in an HDFS cluster. It is affected by factors such as bandwidth, latency, and network topology.

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HDFS File System

A hierarchical file system designed for storing and managing large data sets across multiple machines (Data Nodes) in a distributed manner. The Name Node acts as a master node, managing the namespace and block mapping.

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Name Node Responsibility

The Name Node is responsible for managing the file system namespace, tracking and assigning block locations, and managing the replication factor. It also oversees the health of Data Nodes.

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Data Node Role

Data Nodes store and manage blocks of data. They also communicate with the Name Node to report their status and receive instructions for data operations.

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Block Replication (Why?)

Data blocks are replicated across multiple Data Nodes for fault tolerance. If a Data Node fails, the data can still be accessed from the remaining replicas.

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Secondary Name Node Purpose

It periodically creates a checkpoint of the Name Node's metadata, including the file system image and edit log. This allows for faster recovery in case of Name Node failure.

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Data Node Heartbeat

Data Nodes periodically send heartbeat messages to the Name Node to indicate their status and availability. This enables the Name Node to detect and handle potential node failures.

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HDFS Read Workflow

Clients connect to the Name Node to request data. The Name Node identifies the location of the requested block and directs the client to read directly from the Data Node. Clients can retrieve missing blocks from other Data Nodes in case of failures.

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HDFS Read Design (Advantages)

The HDFS read design prioritizes scalability, efficiency, and fault tolerance. It avoids bottlenecking the Name Node by allowing clients to read data directly from Data Nodes.

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HDFS Write: Client Role

The client connects to the Name Node to obtain data node locations for writing data. It then writes blocks directly to the specified data nodes with the desired replication factor.

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HDFS Write: Name Node Role

The Name Node tells the client which data nodes to write to and manages block replication. It also handles data node failures and ensures data consistency.

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HDFS Replication Strategy: Single Rack

Placing all replicas of a data block on the same physical rack. This minimizes write bandwidth but increases risk of data loss if the rack fails.

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HDFS Replication Strategy: Different Racks

Distributing replicas across different racks to maximize fault tolerance. This strategy increases write bandwidth but reduces read bandwidth.

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HDFS Web UI

A web-based interface providing a graphical overview of the Hadoop cluster, including Name Node and Data Node status, file system usage, and other metrics.

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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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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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