Exchange 2010 DAG

Hi,

I m having the exchange 2010 DAG setup in my environment.i need a backup of this setup.my setup is

== >  CAS/HUB in one(1) machine .

===> Mailbox Role in another two(2)machines.

How can i install the backup Exe ? BE  install on  any one machine or all machines?

i have trailware BE .

can any body explain / any related help documents.

Regards

Gouse