Hi,
I have a RaQ4i with my own DNS (ns1.mydns.com). Now, I want to rent another RaQ and want to use ns1.mydns.com also for the new server.

Is it possible to have only a pair of DNS and use them in many servers.

Thanks in advance for your help.

Should be no problem. Just specify that server (ns1.mydns.com) as the ns for the domain, and then enter the records on the ns1 server. Just be aware that this will create more load on your original server as it will be responding to DNS requests for domains on both servers.

One suggestion - I would set up ns2.mydns.com on the second server, and list it as secondary for all of your domains - that way if server #1 crashes, you'll have a b/u - and a DNS error won't get cached!

There are some GREAT posts in here on setting up secondary DNS - just do a search and you'll learn a lot.