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Old February 7th, 2013
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Quote:
Originally Posted by Sleepless View Post
While I'm sure your intentions are in the right place here, you should surely take into account what else small piece sizes do to big torrents. First off the torrent file will be huge. Second, while yes if you are interrupted while downloading a piece you will most likely lose that data, lets do a little math having e.g.

A 8.53GB torrent. In my case I lost 55.18MB while downloading it. It was piece size of 2MB = 4366 pieces. Protocol on a bigger piece torrent will generally use around 0.3% (messages back and forth between clients, which depend on a lot of things) approx. 26.2MB

You want 512KB pieces i.e. 17464 pieces. Well that means 4 times as many messages. So 26.2MB x 4 = 104.8MB so 78.6MB more than with 2MB piece size.

Now let's go back to the beginning where I said I lost 55.18MB. Let's say you lose 4 times less with 512KB pieces, so 13.8MB.

512KB pieces = 104.8MB + 13.8MB = 118.6MB waste
2MB pieces = 26.2MB + 55.18MB = 81.4MB waste

IMHO the uploader should have made the torrent 4MB pieces as around 2000 pieces works quite well when minimizing wasted data. But you probably use some bad client like Limewire, so you can't see all the overhead used on small sizes.
Coincidentally just today I noticed two torrents with similar issue, same title but one was DVD-DL (7.5 GB), the other BD (24.74 GB). This is a more extreme example. The DVD-DL torrent used 256 KB pieces. The overhead was an astounding 10-12 KB/s lost to messaging overhead.
Whereas the BD torrent used 4 MB pieces, barely any noticeable overhead at all. I guess divide the 10-12 KB/s by 16 to get the overhead of the BD torrent. I decided to kill seeding the DVD due to so much overhead bandwidth thrown away for nothing. I am instead seeding the BD version. My public torrent ratio is 1.5 and private torrents over double that so hopefully I'm excused. (There are several other same content DVD torrents anyway.)

BD (24.74 GB), 4 MB pieces: overhead not noticeable; negligible. . (5,901 pieces) . (About 0.02 GB extra download.)

DVD-DL (7.5 GB), 256 KB pieces: overhead 10-12 KB/s. . ( approximately 30,000 pieces) . (stats of extra download not available since I killed it. But no doubt, extra waste-age on top of this for both seeders and leechers is a phenomenal amount. ie: 36-42 MB per hour wasted in overhead for the seeder alone. 10 hours seeding this was enough for me. This particular torrent represents very high inefficiency.)



Another point in mind about public torrents is that you may get all kinds of torrent programs and versions (some very old) and their bad data transfers can be high. This is something you do not normally see at private torrent sites where the sites are often strict on which torrent programs and which versions are allowed to use their trackers (for many reasons.) I know Vuse has an auto-banning function for clients that send more than a certain amount of bad data. This can be customized.
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