Say if I have a subomain hosted on one server, then the main site will be on a different server. Here is an example: domain.com is hosted on dedicated 1 sub.domain.com is hosted on dedicated 2 Say if sub.domain.com received 100K visitors, and the dedicated server being used by sub-domain.com can handle it. Will the main site dedicated server be affected?
No as the first server will receive a few dns requests and that is it, as everything will just be directed to the second server without even going via the first server.
It won't receive many requests, DNS requests are cached, usual at ISP Level or some big business/networks have their own DNS cache. Also DNS requests are quite minimal and you would not really notice any kind of traffic via them.