[bittorrent] Why are blocks smaller than pieces?

Guido Seifert tanuki64 at gmx.de
Sat Sep 8 19:01:01 EDT 2007


> Well, typically requests (and therefore blocks) are 16kb (so that slow peers
> and high latency links don't cripple swams), compared to typical piece
> sizes, which are between 128k to 4mb or more (no real limit).
> 
> Consider a 20gb torrent with 16kb pieces, the consequent size of the
> .torrent file, and more importantly, the protocol overhead required to send
> massive bitfields and the numerous HAVE messages.

Yeah, the reason for would be quite some overhead.

[...]

> Hope that's useful. Certainly that is a weakness neccessitated largely by
> the dynamics of sending (very) large files over potentially slow links, but
> it can be worked around.

This sure is useful and not too difficult to implement. I am by far not that 
advanced with my client that I can yet use it, but the sooner one considers such 
problem in a new design, the better. :-)
 
Guido





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