One person seeding a really popular file once will now be able to download a bunch of other files without seeding.
But this isn't actually the most usrful result! In this model distributing 100MB of GoT is as valuable as distributing 100MB of some file with only 2 or 3 seeders. But those Megs are not equivalent if the objective is to maximize availability of files.
Being the seeder of last resort on a rarely (but still downloaded!) file is way more valuable than being the 100k'th seeder on some new TV show.
This isn't necessarily what the GP was getting at but is a good example of seed ratios not having the best incentives.
And this is why many trackers have departed from purely ratio-based requirements.
A couple examples:
"Required ratio" based on percentage of "snatched" (i.e. downloaded) torrents you are seeded. For example, if you're seeding all torrents you have ever downloaded, your required can be 0 (instead of initially common values of 1 or 0.9).
Ratioless: no ratio requirements, but you must instead seed all torrents for a specified time.
Among people involved in private torrent communities it's fairly well-known that a purely ratio-based system does not provide the best incitements (which would be a library of content that is as diverse and well-seeded as possible).
Anyway, the main reason many prefer private trackers to public is not only because of enforcement of contributing back, but because of rules that ensure that the available content has high quality (i.e. curation).
One way some trackers combat this is with bonus points that are awarded based on how poorly seeded a torrent is. (Poorly seeded torrent -> More bonus points)
One tracker I'm a member of combats this two ways.
1. You get one point for seeding a torrent per hour, up to 10 total. You can exchange 1,000 pts for 10GB of upload credit (e.g. improves your ratio). The torrents don't need to actually be downloaded by anyone to count. This seems to work well as torrents that are weeks and weeks old still have seeds.
2. Popular torrents are listed as 'FREE', which means that downloads don't count against your ratio, but upload is still counted. So anything that gets swarmed gets lots of activity.
I always thought it was a pretty silly system too. You end up in a situation where you want do download something, other people want to upload that thing but you don't do it because you don't want to ruin your ratio.
This in turns means that these other people don't increase their ratios and end up in the same situation. You have an artificial 0-sum game for absolutely no good reason. Then you need freeleech periods or bonuses to make up for the ratio credit "deflation".
I think it would make more sense to punish people who never seed (seeding if nobody is downloading is fine, you can't do anything about it) and incite people to seed torrents with a low seed count.
I agree. In the only private tracker I use, you get rewarded for both the amount you've seeded and also for the number of torrents you're seeding (even if nobody downloads them).
Depends on the trackers, most of the time you need an invite.
Private trackers are often topical, either focusing on movies, video games, music, ebooks etc... So if you want an invite to these you just need to hang out with people who share these interests and then ask around. IRC is a good place to start in my experience.
Some semi-private trackers also have periods where registration is open to all.
Some trackers have periods in which they have open registrations; there are a few sites which track these (like r/OpenSignups), so I subscribed to one and registered to those that seemed interesting.
Otherwise, you have to get an invite by an existing user; if you don't know any, I think the best bet is to lurk forums and IRC channels and beg for one. I never actually went that route, though.
What.cd was one of those - you literally had to get an invite from friends (inept as you that didn't work for me) or apply via IRC (can do that!), including an interview to make sure that you understood the rules and had a basic understanding of audio formats, encoding parameters.
People that brought you on were supposedly responsible for any problem you caused..
The economics of most private torrent sites is fucked beyond belief if you haven't participated. I've only seen one paper on it from Microsoft research. Maybe more has been written on it that I haven't seen.
The idea is to get users to seed, rather than just leach and then shut off their client. Where does saving bandwidth come into the picture?