This question is to anyone who is familiar of caching systems (i mean content delivery network caching systems).

What I need to learn and analyze are the basic concepts and naive methods of caching a video file when at high demand. I want to compare some novel methods that involve social network assisted "caching policy/system" with something simple like caching to the nearest geographical location. I have no prior knowledge to caching in content delivery networks. e.g. how does youtube cache videos. even a textbook or tutorial reference would be helpful.

Just trying to formulate, I have N servers and M users. Given R cities, I know the geographical map of the server locations and thereby the latency. If certain cities show high demand, how does a cache management system cache multiple copies of the video file for access? of course with minimum cost (minimum number of identical copies on multiple servers)

thanks!!