This post lists pitfalls and lessons learning when configuring and tuning Hadoop.
Hadoop with IPv6
One good practice is to disable IPv6 on servers in the Hadoop cluster.
Hostname vs. IP
Hostname is preferred. Using hostname instead of IP address may possible solve some problem magically.
Java Virtual Machine
Take care whether the JVM on all nodes are friendly with Hadoop. In case there are some nodes are configured with wrong JVM, problems may flow up.