Using network topology script to make Hadoop rack-aware

Hadoop has the concept of "Rack Awareness". Administrators are able to define the rack of each DataNode in the cluster. Making Hadoop rack-aware is extremely important because:

• Rack awareness prevents data loss

• Rack awareness improves network performance

In this recipe, we will describe how to make Hadoop rack-aware and why it is important.

Getting ready

You will need to know the rack to which each of your slave nodes belongs. Log in to the master node as the user who started Hadoop.

How to do it...

The following steps describe how to make Hadoop rack-aware:

1. 1. Create a topology.sh script and store it under the Hadoop configuration directory. Change the path for topology.data, in line 3, to fit your environment:

   hadoop@master1$ vi $HADOOP_HOME/conf/topology.sh
   while [ $# -gt 0 ] ; do
   nodeArg=$1
   exec< /usr/local/hadoop/current/conf/topology.data
   result=""
   while read line ; do
   ar=( $line )
   if [ "${ar[0]}" = "$nodeArg" ] ; then
   result=...