Dns cluster, This is where you have dns hosted on 2 separate servers (ie, ns1 on server1, and ns2 on server2). While this is good for redundancy, the disadvantages usually outweigh the benefits.
First, it’s important to realize that DNS alone rarely crashes. Also, if the server goes down and the DNS of the other server is still up, your sites will still be down. So redundancy just for DNS alone isn’t really beneficial.
The only situation where this would be beneficial is if you have redundancy for the site’s www and/or email, then having redundancy of DNS would be helpful.
But there are many disadvantages of clustering the dns. Although the cpanel dns clustering system has improved it’s stability over time, a common issue is that if an error occurs on one server’s dns and causes it to fail, it will get replicated on the other server’s dns and cause that to fail too. Also, as the cluster gets larger over time, it starts to slow down the startup and restarting of the dns system drastically depending on how many sites are on the server.