If you have custom content on your server, it is strongly recommended to also have a fast download server. A fast download server (also called a FastDL server, or a redirect server in the Unreal world) is a HTTP site that mirrors the custom assets used by your game server. Downloads directly from the game server are slow, regardless the connection speed between the server and the client. Once you have a fast download server set up, you can have your clients download files from it rather than directly from the game server.
To save bandwidth and speed up downloads, you can use the bzip2 format to compress any file on the download server. For example, you would compress maps/ge_map.bsp into maps/ge_map.bsp.bz2, and upload the .bz2 file to your fast download server.
The console variable that tells clients to download from an HTTP site is sv_downloadurl "http://www.example.com/my_folder/“ – note the double quotes around the URL. In this example, my_folder is equivalent to the gesource folder. If this console variable is empty, files download directly from the game server as long as the file's size does not exceed net_maxfilesize mebibytes.
Having a fast download server does not automatically make clients download your custom files. To learn how to make files download for a certain map, see write_a_download_list.
Some tools exist to automatically sync files between a game server and fast download server, such as SourceRSC.