why do you need drupal?
for this to be done correctly, mirrors shouldnt need anything apart from the files imo.
The single map DB php script should redirect players requests to the correct file download link, even if its on another server.
if one server goes down, it just uses another..
if the main is down, the main php script is also mirrored on the other links, so that a downloader can point to that instead.
need a diagram?