Re: What to do when an A record is missing ???

[Chris Coyier]

Yeah, the only time you really need to specifically mess with the A record on a subdomain is if you’ve got multiple servers set up for different purposes. Ie you host your main site on a fast local box with fast CPU and lots of RAM but not much data transfer, and you have your media downloads on a separate box that’s less powered but with a ton of bandwidth. You’d create an A record for media.domain.com to point to this other server.

I think Chris actually did a little tutorial on this a while back.. I learnt it from somewhere anyway! Was surprisingly easy to implement.