[tahoe-dev] Recombinant Hashes

David-Sarah Hopwood david-sarah at jacaranda.org
Fri Feb 12 06:38:19 UTC 2010


Zooko Wilcox-O'Hearn wrote:
> On Thursday, 2010-02-11, at 22:31 , David-Sarah Hopwood wrote:
> 
>> According to this ticket: <http://allmydata.org/trac/tahoe/ticket/ 
>> 678>, the FEC code that Tahoe uses also has the property that the  
>> content of some initial subset of shares does not depend on the  
>> total number of shares. If that's correct, it's not clear to me why  
>> it it's not also classified as a fountain code, although I've never  
>> heard of Reed-Solomon codes referred to as fountain codes.
> 
> Perhaps because there is a fixed upper limit on how many unique  
> shares we can generate. The erasure code library that Tahoe-LAFS uses  
> -- zfec -- maxes out at 256 shares. The library from which zfec was  
> derived also included a variant that maxed out at 65536 but encoding  
> and decoding would be slower.

OK, that explains it.

-- 
David-Sarah Hopwood  ⚥  http://davidsarah.livejournal.com

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