[Tux3] Comparison to Hammer fs design

Maxim Sobolev sobomax at FreeBSD.org
Wed Aug 6 17:54:15 PDT 2008

Matthew Dillon wrote:
    Well, you've described both sides of the debate quite well.  I for
    one am in the 0-risk camp.  ReiserFS got into trouble depending on
    a collision space (albeit a small one).  I did extensive testing of
    64 bit collision spaces when I wrote Diablo (A USENET news system
    contemporary with INN, over 10 years ago) and even with a 64 bit space
    collisions could occur quite often simply due to the volume of article
This is due well-known mathematical property, called birthday problem or 
birthday paradox. As a result of that property for ideal hash function 
of size N bits you only need 2^(N/2) random inputs to generate a 
collision with sufficient probability. Therefore, for 64 bit hash 
function you will get one collision for approximately every 2^32 inputs.



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