Availibility

[paddy_kaustubh]

I have a question. I am sorry if this is not the board for it.

Here goes:

How is it that Availibility is more than number of peers?

doesnt avaiilbility mean the no of copies?

for eg: i am downloading iron maiden and it has 24 peers but availibility is 27.997!

[Switeck]

Each connected seed adds +1 to availability.

This includes YOUR seed if you are in fact seeding that torrent instead of downloading.

[Firon]

Multiple unique copies can be distributed among peers as well (basically limited by how many copies of the rarest piece exist)

[andr_gin]

As far as I know the availability is the numer of times the least available piece has:

Availability of 25.6 means that every piece have 25 OR MORE sources and 60% of the pieces have 26 OR MORE pieces. Is this correct?

For the pieces all peers and seeds are counted. A seed has 100% so it adds +100%.

[DreadWingKnight]

25.6 = 25 complete sets, largest incomplete set is 60%

Complete sets can exist without seeds.

[atlantisisdead]

I am a newcomer to anything torrent. One thing forgotten over time is how little a new person knows. I had read that "availability" represented the percentage of the complete torrent available for all peers to download regardless of how many are present. What matters is how many of the pieces are present between those peers. For instance, when a peer has 94.7 percent of the file, and no one has any pieces beyond the same ones he has, then .947 will show in the availability. When that peer leaves, if no one has had time to download his entire 94.7 he was hopefully uploading, he takes his 94.7 with him and the availability will reduce down to the percentage of the full torrent shared between the remaining peers. In my case, "64.something," and then he/she returned and the availability went back up to 94.7, presumably they are back to try to get that last 2.3 percent.

I also read that if availability is less than 1.0, then it is unlikely anyone will ever download the entire torrent, unless something extenuating comes up, like the torrent provider "reseeding" the torrent... or someone who previously downloaded it returns to seed. Unlikely. I read something about a super seeder, but not sure now what it was about.

Do I misunderstand any of this?

[Ultima]

You understood it more-or-less perfectly.

Super-seeders masquerade as regular peers, meaning they don't tell other peers that they actually have the full set of data. This is used in an attempt to control what pieces other peers receive from that seeder. If implemented well/correctly, the super-seeder should be handing out every single piece at most once to the swarm (unless a previously-distributed piece is missing from the swarm again?), and to different peers, before it repeats itself. This generally improves swarm life for torrents with few seeders, since (theoretically) no one peer can amass most of the pieces before other peers and potentially leave (because they're leeches, or something).

[atlantisisdead]

I see! And so, if more peers receive full downloads faster by not having to wait for all the pieces to be available as long as otherwise (without the super seeder), the odds of more seeds and seeders increases as well.

uTorrent seems to be set to upload more than download, and my share ratio is 1.83 even though I only have 1/3 of the file so far. However, this seems to me to be good for appearance, and keeping a good reputation, but only actually beneficial to the swarm if I were to seed the full torrent for awhile after I receive all of it, instead of just looking at my share ratio and saying "I did my bit" and leave as soon as the download is done.

Actually, that should end in a question mark, because I am pondering.

Also, how is it that it is not infrequent to see a torrent with availability at 97.4 percent or close to that number? Seems to happen a lot, that last little piece not there.

[Ultima]

No, it's not to look good or keep a good reputation. µTorrent is always uploading while it's downloading, and if you just happen to not be able to download much (because few peers are giving you what you want), then of course the upload count will eventually pass the download count. [NOTE: I think I misunderstood you]

If you see torrents with less than 1.0 availability often, then you're probably frequently downloading old torrents (where everyone's already left), or very new torrents (where the seed is super-seeding without having sent a complete copy out yet).

Edit: If everyone did upload more than 1.0 ratio, it does automatically help the swarm -- that's if everyone (or a large majority of peers) uploads that much. Otherwise, as you said, staying around where there aren't enough seeds would probably be more beneficial indeed.

[atlantisisdead]

Very helpful, thank you. The more I learn, the more I need to know. LoL.

[Switeck]

A lot of people are sharing files that have been damaged by semi-hostile software on their computer. The most common examples are Media Players that change the MP3 tags on audio and video files...resulting in the last (tiny?) section of those files automatically failing the hash matching check. Many are blissfully unaware of this...as the file PLAYS for them, they're just unable to share the ending portion of the file for OTHERS to get it to work!