People operate mirrors out of different reasons, this could be purely altruistic to support open source communities, or to reduce incoming traffic by providing local clients with an internal package source, or to tilt the in/out ratio of the internet uplink. What ever the reasons are, they are all associated with the usage of outbound traffic and local storage size, in addition to occupation of other hardware and administrative resources. We will consider traffic and storage requirements as the costs and outgoing traffic as the profit (to the general public or an organization) a mirror service provides.

Here are the most used mirrors in 2015:

Kiwix on rank 2 has only been mirrored since March 2015, so it generated that amount of traffic in only 9 and a half months - it might well take over the top spot next year. The Ubuntu release ISOs dropped out of the Top 10 for IPv4. As is to be expected, the CCC conference recordings generate extremely peaky traffic after CCC events - setting a new record high with 11.3 TB in just one day on December 30 (after 32C3). It might even have made a little bit more, but unfortunately the webserver ran out of threads because someone apparently distributed web-torrent-files with 64 KB of chunksize.

While we publish daily stats for all of our mirrors at https://ftp.fau.de/cgi-bin/show-ftp-stats.cgi, there is currently no aggregation over a whole year. So here are the most used mirrors over the whole year:

The list is slightly different for IPv6.