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

Managing the NameNode


Let's do some more risk reduction. In Chapter 6, When Things Break, I probably scared you when talking about the potential consequences of a failure of the host running the NameNode. If that section did not scare you, go back and re-read it—it should have. The summary is that the loss of the NameNode could see you losing every single piece of data on the cluster. This is because the NameNode writes a file called fsimage that contains all the metadata for the filesystem and records which blocks comprise which files. If the loss of the NameNode host makes the fsimage unrecoverable, all the HDFS data is likewise lost.

Configuring multiple locations for the fsimage class

The NameNode can be configured to simultaneously write fsimage to multiple locations. This is purely a redundancy mechanism, the same data is written to each location and there is no attempt to use multiple storage devices for increased performance. Instead, the policy is that mltiple copies of fsimage will...