I am new to exchange 2010 but from what I gather there are 4 roles (CAS, hub transport, mailbox, unified messaging), my question is if you seperate these onto 4 different servers, do you have to install exchange software on all 4 servers. I am looking at it from a patch management angle, i.e. have you got 1 server to apply exchange specific patches to - or up to 4? Or is it common to install all 4 roles onto the same server (with the exchange application installed on top of the OS)?
If you only install exchange on 1 server - which is it, given the number of different roles in the exchange architecture?