Prepare yourself for a very long and detailed article by Lars George explaining how to correctly configure the number of server side threads (and sockets used for data connections)— the HDFS dfs.datanode.max.xcievers configuration option. Even if I’ll be giving you the final secret formula, I strongly encourage you to read the details:
This blog is called myNoSQL and it is written by me, Alex Popescu, a software architect with a passion for open source and communities.
It records my readings, learnings, and opinions on NoSQL databases, polyglot persistence, and distributed systems -- subjects that I'm passionate about.
The opinions expressed here are my own, and no other party necessarily agrees with them.
If you feel I'm biased, I probably am.