I was reading the following FDS paper:
and it says that the the following hash function does not distribute things uniformly (instead it creates a binomial distribution):
$$i = (hash(g + t)) \pmod n$$
while the following did distribute things uniformly:
$$i = (hash(g) + t) \pmod n$$
Why does the above distribute things evenly while the other one doesn't?
g = is the global UID for a blob
t = tract number. (tract is the measure/units of reads and writes to a blob).
n = is the number of tract servers or a multiple of the tract servers.
hash = SHA-1 (according to the paper)
Title: Flat Datacenter Storage
Author(s): Edmund B. Nightingale, Jeremy Elson, Jinliang Fan, Owen Hofmann, Jon Howell, Yutaka Suzue
Institution(s): Microsoft Research, Univeristy of Texas at Austin