There are couple of benchmarking tools which come with Hadoop Distributions like TestDFSIO, nnbench, mrbench, TeraGen or TeraSort.
For Network bottlenecks and IO related performance issues TestDFSIO can be used to stress test the cluster.
NNBench can used to do load test on NameNode by creating, deleting, and renaming files on HDFS.
Once the cluster passes TestDFSIO tests, TeraSort benchmarking tool can be used to test the configuration. Yahoo used TeraSort and created a record of sorting 1PB of data in 16 hours on a
