Hi @Aishwarya Dixit, pe or "Performance Evaluation" is a tool based on MapReduce to test read/writes to HBase. nclients means that 10*nclients mappers will be started to run the supplied pe command. Example:
hbase pe randomWrite 2
2017-09-02 01:31:17,681 INFO [main] mapreduce.JobSubmitter: number of splits:20
starts a MR job with 20 mappers and 1 reducer. So you can start with a small number like 1-3 to make sure HBase works as expected, and then increase it to about max number of mappers you can run on your cluster divided by 10. Of course you can use a larger number, but then mappers will run in multiple "waves".