Hi to provide redundancy for CAS and HT, Iwill install both role onto two physical servers. The maximum memory and number of processeurs recommended is different for each role! the question, we is limited by the minmum recommended for both servers or we can use the maximum? CAL max recommended is 8Go for RAM and 4x processors core HT max Recommended is16Go for RAM and 8x processeurs core as both roles are deployed on the same server, witch value can be used for sizing? there are any disadvantage, to install both roles on same machine? thinks

In the ideal environment all roles will be installed on single servers which are scaled 100% to the recommended / best practice specifications. However in real life, it just comes out to being too costly in terms of hardware requirements as well as admin / maintenance overheads. As such many Exchange deployments out there are combining the HT/CAS roles onto single servers & the spec used for those roles is largely scaled & dependant on how busy we anticipate these servers to be, ie number of users on owa/activesync/anywher access, emails transfered daily etc. Taking into consideration the fact that you are going to load ballance them in some way or another, either dns round robin, hardware load balancing or MS NLB the servers should be takling roughly 50% (each) of the total network load per day. Having taken the above into consideration its upto you to look at how you want to spec your servers - in my case for a 150+ user network running all 3 server roles I have deployed a single server with dual quad core processors & 12 gb ram, this works extremely well for the client. Why not look at it this way, if you used 8GB to start n found it didnt perform so well its always easy to add more ram to improve this, where as if you bought the additional ram initially & it wasnt required then there's a lot less out there you could do with it.