How does it work the Secondary Server?

[Ricardo Martinez]

Hello list.
	I have a general question about how the seconday/slave server works.  Please correct me if i'm wrong.
I have two DNS bind servers, one is the primary server and the other, as you could guess, is the secondary/slave server.   My question is related to the way the requests are procesed in 

a.- Normal Situation
b.- Failure of the Primary Server
c.- Failure of the Secondary Server

Can someone explain to me how this work, i'm a little bit confused especially when a failure occurs.
For example in normal situation the request from the root servers arrives 50% to my primary server and 50% to my secondary, isn't?  If so, what's the idea of a secondary server if primary goes down? it will keep receiving requests even if the server is down? 

Hope that someone could explain to me this.
Thanks in advance

Regards,
Ricardo.-