Adding a Second Server

[Arhineus]

Up until just recently, we've only had 1 web server running, and it was setup for us previously.

This server is setup as below.

Hostname: hostname1.domain.com
Primary Name Server: ns1.domain.com
Secondary Name Server: ns2.domain.com

The new server I'm setting up as follows.

Hostname: hostname2.domain.com
Primary Name Server: ns3.domain.com
Secondary name Server: ns4.domain.com

1) How exactly does the 'clustering' feature work, and what are the advantages and/or disadvantages of using it?

ADDITION

Here's the second part of my question.

I have domain1.com already on hostname1.

I want to create sub.domain1.com on hostname2.

How do I get it so that when the user enters sub.domain1.com it will take them to the proper site? Right now I'm just getting a Server Not Found error.

[gorilla]

To point the subdomain from your old server to your new server you just need to edit the DNS in WHM on your oldserver and point the sub to the installation IP of the sub on the new server