We use a redundant DNS cluster for greater stability and speed.
Each nameserver resides in a different data center, so each nameserver is physically separated from the others.
This way if one of the nameservers has a problem the site stays online because it is served by the other servers in the cluster.
We can use the same nameservers for all our servers and if we have to move your site from one server to another we can do it without any downtime.
We also used the cluster to set up a secondary MX
, which we offer for free with all shared hosting solutions.