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 – adding an additional fsimage location


Let's now configure our NameNode to simultaneously write multiple copies of fsimage to give us our desired data resilience. To do this, we require an NFS-exported directory.

  1. Ensure the cluster is stopped.

    $ stopall.sh
    
  2. Add the following property to Hadoop/conf/core-site.xml, modifying the second path to point to an NFS-mounted location to which the additional copy of NameNode data can be written.

    <property>
    <name>dfs.name.dir</name>
    <value>${hadoop.tmp.dir}/dfs/name,/share/backup/namenode</value>
    </property>
  3. Delete any existing contents of the newly added directory.

    $ rm -f /share/backup/namenode
    
  4. Start the cluster.

    $ start-all.sh
    
  5. Verify that fsimage is being written to both the specified locations by running the md5sum command against the two files specified before (change the following code depending on your configured locations):

    $ md5sum /var/hadoop/dfs/name/image/fsimage
    a25432981b0ecd6b70da647e9b94304a...