How does nginx weighting work?

[highclass99]

upstream myCloud{
  server 10.0.0.1 weight=10;
  server 10.0.0.2 weight=20;
} 

For 30 sequential requests,
will it work like
A.
10.0.0.1 10.0.0.2 10.0.0.2 -> 10.0.0.1 10.0.0.2 10.0.0.2 -> ... total 10
times repeat

or will it work like
B.
10.0.0.1 ... 10 times repeat -> 10.0.0.2... 20 times repeat

Because if it works like A, it would be helpful to use large numbers to fine
tune weighting.
But, if it works like B, it would be harmful to use large numbers to fine
tune weighting.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,261982,261982#msg-261982