Book Image

Hadoop Beginner's Guide

Book Image

Hadoop Beginner's Guide

Overview of this book

Data is arriving faster than you can process it and the overall volumes keep growing at a rate that keeps you awake at night. Hadoop can help you tame the data beast. Effective use of Hadoop however requires a mixture of programming, design, and system administration skills."Hadoop Beginner's Guide" removes the mystery from Hadoop, presenting Hadoop and related technologies with a focus on building working systems and getting the job done, using cloud services to do so when it makes sense. From basic concepts and initial setup through developing applications and keeping the system running as the data grows, the book gives the understanding needed to effectively use Hadoop to solve real world problems.Starting with the basics of installing and configuring Hadoop, the book explains how to develop applications, maintain the system, and how to use additional products to integrate with other systems.While learning different ways to develop applications to run on Hadoop the book also covers tools such as Hive, Sqoop, and Flume that show how Hadoop can be integrated with relational databases and log collection.In addition to examples on Hadoop clusters on Ubuntu uses of cloud services such as Amazon, EC2 and Elastic MapReduce are covered.
Table of Contents (19 chapters)
Hadoop Beginner's Guide
Credits
About the Author
About the Reviewers
www.PacktPub.com
Preface
Index

Time for action – examining the default rack configuration


Let's take a look at how the default rack configuration is set up in our cluster.

  1. Execute the following command:

    $ Hadoop fsck -rack
    
  2. The result should include output similar to the following:

    Default replication factor:    3
    Average block replication:     3.3045976
    Corrupt blocks:                0
    Missing replicas:              18 (0.5217391 %)
    Number of data-nodes:          4
    Number of racks:               1
    The filesystem under path '/' is HEALTHY
    

What just happened?

Both the tool used and its output are of interest here. The tool is hadoop fsck, which can be used to examine and fix filesystem problems. As can be seen, this includes some information not dissimilar to our old friend hadoop dfsadmin, though that tool is focused more on the state of each node in detail while hadoop fsck reports on the internals of the filesystem as a whole.

One of the things it reports is the total number of racks in the cluster, which, as seen in...