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Imagine that we have two torrent files. They contain similar, but not exactly the same files.
For example, one torrent is same as the other, but has some text files at the end of it.
Knowing that these two torrents will probably share most of the pieces, are BitTorrent clients able to exchange these pieces with other torrents?
I assume that this will only be possible if peers ask for any pieces on the tracker which has the right hash, instead of asking for specific portions of the currently downloading file.
Example diagram:
Edit - Just to be clear:
1. I am not referring to running multiple instances of clients on a machine in order to download a file which appears in two torrents.
2. I am not referring to downloading the same file with two different torrents.
3. What I'm asking is, if two different torrents, by chance, contain identical "pieces", not files, can the pieces be used interchangeably from a tracker to another?
4. To simply put it, I'm asking if it is possible for a single client downloading a single torrent file, to retrieve pieces from another torrent, assuming that those pieces are identical.
(Both torrents by chance include a piece with a same hash.)
For example, if I am only downloading torrent A, I will need blue and green pieces. Since Torrent B contains green and yellow pieces (not files), could it be possible to retrieve some green pieces from Torrent B?
If I am correct, each piece should have its own hash, so, if both Torrent A and Torrent B contain the same piece, they should be able to use that same piece. The peer could ask for the same pieces by their hashes on a tracker, and if so, identical pieces with identical hashes can theoretically be shared between torrents.
The chances of two torrents having the same piece is irrelevant, I'm asking you to accept that we have this situation, and tell me what does the Torrent protocols do if this is met.
David Refoua
Posted 2016-01-31T03:50:02.877
Reputation: 239
No, because nearly identical, wouldn't result in identical hashes – Ramhound – 2016-01-31T04:17:08.220
Doesn't each piece have its own hash? I'm not asking for the entire file by its hash, I know how it works. What I'm trying to ask is that, will the peer ask for the pieces by their hashes? If so, identical pieces with identical hashes can theoretically be shared between torrents. – David Refoua – 2016-01-31T05:16:51.903
1BitTorrent does not work like the way you think it does. The pieces together make up the hash of the entire torrent, all files and their pieces, most torrents are not made up of files you could replace. In most cases your going to have a single .ISO file,perhaps some text files. – Ramhound – 2016-01-31T06:37:34.883
So, if we have Torrent A which contains .iso + txt, and torrent B which only contains .iso file, if seeders leave Torrent B, can the client get pieces from Torrent A assuming up until the text, other pieces are identical? People suggest adding trackers for Torrent A to Torrent B in these situations, and this works. – David Refoua – 2016-01-31T06:45:12.027
If the text files were identical and had the same hash, and the .ISO files were identical and has the same hash, then the torrent would be identical. I don't understand your question. If you are going to say what other people say, provide us a link, so we can read what they actually said. – Ramhound – 2016-01-31T06:47:30.753
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@Ramhound Thanks, I posted two links. Also, regarding your comment, I'm sure that I said Torrent A contained every file in Torrent B, plus files that were not in Torrent B. So, one torrent contains all of the other torrent's files, plus some extra files. – David Refoua – 2016-01-31T06:53:03.733