why are seeds neccesary?

[xxxxx]

when downloading a file it is nessary to check to see that there is a seed (a peer with a complete file) for the leeches (peers with incomplete files). this is confusing to me because i would believe that the tracker should be able to distribute the constituant parcels of the file (250 K per parcel) to divergent peers in order to minimize redundant downloading. these peers with incomplete files should be able to upload the remaining parcels of the file to each other, even if no one peer has a complete file.
in other words, if two peers each have 50% of a file, bittorrent should be able to allow them to upload each other's parcels to complete each´s file.
this would make it unneccesary for a person with a complete file to be online (an advantage since once the download is complete a person would not be as likely to remain connected for as great a period of time as the download took to complete).
is this an inheirant limitation to bittorrent, or could the tracker be modified to perform this function (i think bittorrent is great, and always leave my downloading window open after completion for as long as possible) and how many lines of code would have to be written to change the program to perform this function.

[NoSanninWa]

Seeds aren't necessary. The program works exactly the way that you think it should.

Unfortunately, it is not always true that a complete copy is distributed amongst all of the peers. Seeds are only required either early or late in a torrent's life-cycle. Early on the original copy hasn't been fully uploaded yet. Later on there are only a very few people connected and they only have a tiny portion of the file so they need to request a seed to help them finish after they share the parts that they have.

As long as a file is still popular it is inevitable that there is copy of every part of the file being distributed even if there are no seeds. In this case, no seeds are necessary.

[Shinobu_Maehara]

I downloaded Ebichu completed (all three Torrents)
And my poor Pentium 2/400 torrent server has all three windows open since december 3rd.
It has windows XP running so as long as I don't touch it it'll be stable until I turn it off. :P

It's better to have as much seeds as possible so everybody can leech and share every available part whenever needed.
More seeds, more speed...

I'm currently uploading with an avarage of 60 Kibi's with the torrent server only...
So there are a number of people leeching data from me

[NightWish]

(I was so distracted writing this and slow to respond its probably already been said but heh... I've written it now)

It isn't necessary to check that there is a seed; you can in fact do just as you described and download the whole file from its parts using only incomplete peers. As I understand it the clients announce what parts they have and what they need; so any attempt to manage what they download would have to be done at a client level. Trying to do this processing on the server might load it too heavily or at the very least reduce its scale-ability.

One client (I forget which as I don't use it) has a "super-seed" mode in which a seeder can force rare parts of the file to be disseminated before it gives up less rare parts... thus helping increase the overall "presence" of the file. This is supposed to be bad for normal downloading though... I don't have all the technical details, but generally what you describe does happen so long as the torrent is big enough.

[NoSanninWa]

Originally Posted by NightWish

One client (I forget which as I don't use it) has a "super-seed" mode in which a seeder can force rare parts of the file to be disseminated before it gives up less rare parts... thus helping increase the overall "presence" of the file. This is supposed to be bad for normal downloading though... I don't have all the technical details, but generally what you describe does happen so long as the torrent is big enough.

That is not what super-seed mode does. Super-seed mode disseminates part 1, then part 2, then part 3... part last. In order. This is great if you are the first and only seed becuase you know that you are giving every part of the file to someone without any duplication of effort. (Without this you typically have to upload about 150% before a second seed forms.) This is awful for normal downloading because it completely disregards the rarity of the parts or what people actually want.

[NightWish]

Originally Posted by NoSanninWa

Super-seed mode disseminates part 1, then part 2, then part 3... part last. In order.

Ah ok... In my defence that isn't quite how this reads.

[NoSanninWa]

Originally Posted by NightWish

Ah ok... In my defence that isn't quite how this reads.

The page you quote describes how it works. It doesn't contradict what I just said. It only cares about rarity of pieces after it has already sent a complete copy.

[xxxxx]

on scarywater and/or other sites it states that a file without seeds will not (not may not) complete. also persons have written that they have downloaded 99+% of a file and then they have had to request someone with the complete file log on.
if bittorent works in the manner that i described how can these things be reconciled.
would not bittorrent have allocated the missing parcels of the file to another peer,
or allow the peer with 99+% to download the missing parcels from the main server.

[Flash_Squirrel]

BT doesnt work *exactly* like you wrote in the first post.

If I have the pieces 1, 2, 3 and 4 and the other peer have the pieces 4, 5 ,6 ,7 we both have 50% of the file, yet no one is able to get the full file since we only have 1, 2, 3, 4 ,5, 6 and 7.

The "server" doesnt upload anything, its just the place where the informations about the file are.

If I have the pieces 1,2,3,4~98,99 and the other have the pieces 1,2,3,4,5~97,98, I will upload them my little piece but they will still have a missing piece 100.

Piece = "parcel"

[acefighter]

i dont seed but i normally leave my stuff on. like fma. day it came out i was one of the first to dl it. baka updates updates faster then here. left in on the night and had about 2.5gigs out

[xxxxx]

might there be some way to view an incomplete file? if you have 99.7% of a 24 minute 30 second episode this would mean you are missing 5 seconds of the show.
it would be acceptable in most instances to view an episode missing 5 seconds. some programs, such as explorer allow you to view the file as it downloads. could this be done with bittorrent?

[Flash_Squirrel]

Originally Posted by xxxxx

might there be some way to view an incomplete file? if you have 99.7% of a 24 minute 30 second episode this would mean you are missing 5 seconds of the show.
it would be acceptable in most instances to view an episode missing 5 seconds. some programs, such as explorer allow you to view the file as it downloads. could this be done with bittorrent?

The same old question... Since BT doesnt DL from the beginning to the end but DL in "blocks" if you are lucky you could be able to watch the video at 50% done, if you are unlucky you wont be able to open it even a 99,99...9%
If you miss the header you cant watch the video. >_>

IE allows you to watch the video because it have a progressive way to DL a file, from the header, video and last parts.

[xxxxx]

so you are saying that this has actually been done?

[Flash_Squirrel]

Originally Posted by xxxxx

so you are saying that this has actually been done?

Hmmm? This kind of question? Yes...