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.

Now looking around at what other mirror operators publish, it is very hard to find useful information to guide the mirror selection. Which means, that if you plan on hosting a new project, you have to rely on guesswork to estimate cost vs profit.

Although cost and profit are terms usually associated with currency based units, we will not estimate them using any such metric. We will consider Gigabytes as the unit for storage and traffic and therefore cost and profit.

By combining logged data from the ~50 mirrors we are currently hosting, we are in the position to quantify both cost and profit for each one of them. Be aware that the profit often depends on the geographic location, since many projects use a topology- and geography-aware load balancer like mirrorbrain.

Lets start of with the incoming traffic cost. The average number of GBs that need to be synced from the upstream mirror to ftp.fau.de per day:

We calculated this by summing up all positive changes in mirror size, which is calculated and logged on a daily basis. Since we sync up to hourly, files that get synced and deleted within a day are not covered, nor are files that change.

How about storage costs? Since most mirrors stay around the same size, with a slight increase taking the average size works for most. But some have a tendency to constantly increase (or even decrease), this won’t be correct in all cases.

Let’s have a look at the profit side of things, the outgoing traffic, and put that into relation with the costs. The scores on the right hands side, are calculated by dividing the average outgoing traffic by the average incoming traffic and by the average storage requirement:

What can we learn from this? Small projects can produce a lot of traffic (osmc), especially if they tend to have a small mirror network (libreelec) or a humongous user base (videolan). Big mirrors on the other hand, often produce a lot of traffic in an absolute sense (kiwix, cdn.media.ccc.de), but they are unable to compensate for their storage requirement. For example, the CCC media mirror would have to constantly saturate 2 Gbit/s to get the same traffic/storage ratio as videolan. Although we love outgoing traffic, thankfully they do not. 🙂

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.

The list is slightly different for IPv6.

IPv6 traffic is up – from 7.86% over all mirrors in 2014 to 10.54% in 2015. Absolute IPv6 traffic is also up in 2015 for all mirrors in the Top 10. The share of IPv6 traffic varies greatly between the mirrors.

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.

Still only a small fraction of the traffic is via IPv6, 7.86% over all mirrors and the whole year. CTAN for some reason drops out of the IPv6 list (it would be at #17), its Top10 slot is taken over by Debian (#16 in the total list) which has an unusually large IPv6 share. That large share can be attributed mostly to the local Computer Science Department which has large pools with IPv6 capable Debian machines.

Since the beginning of September, we’ve been creating experimental GeoIP-statistics to see where the users of ftp.fau.de come from. We’re drawing nice maps from the results. You can find these stats from our general ftp statistics page – for days where GeoIP-stats are available, you will find a link to them at the bottom of the page. Here is an example:

As you can see, unsurprisingly most of our users come from Germany. Besides the map there is also a table that show the respective percentages per country – in the map above, Germany accounts for about 50 percent of all accesses. Note that is counting the number of bytes transferred, not the number of accesses.

We also have a map from the stats per Bundesland within Germany:

However, this second map is really mostly guesswork for a number of technical reasons:

• To do the actual dirty mapping work, we’re using GeoLite data created by MaxMind, available from http://www.maxmind.com. This is a free-to-use version of their commercial GeoIP-database, and since they need to make a living from their database, the free version is of course less accurate than the version available to their paying customers. It just returns “unknown” for the Bundesland in roughly about 30% of all cases.
• Due to technical limitations on our side, we’re currently using a rather dusted version of the geoip-mapping library, that for example still has problems mapping IPv6 addresses (although it works sometimes). The quality of the mappings should improve significantly after we update to their current version in the first half of 2015.
• Our logs are normally anonymized, i.e. we do not store the full IP address of a client, but trim (at least) the last octet of an IPv4 IP. This further reduces mapping quality.

Still, we do think it is a rather interesting experiment. While we were expecting most of our users to be from Germany, we found the actual percentage suprisingly high – we had expected some more usage from other european countries.

We have improved the publicly available statistics for our FTP server. You can now see how much traffic each individual mirror makes, and how much of the traffic was IPv6 vs. IPv4. The statistics are available at https://ftp.fau.de/cgi-bin/show-ftp-stats.cgi.

With this, you can see for example that the latest OpenSuSE 13.1 release had a quite significant impact on our FTP: The statistics for 19. November 2013 show that we distributed almost 9 TB for opensuse on that day, more than 5 times the traffic of all other mirrors combined.