1. should i use cluster? 2. What licnese should i purchase (standard or enterprice) 3. if build up redundancy(not cluster) , should i need to have 2 CAS and 2hub transport server or only 2 x server install both CAS and hub transport?

Hello You can do NLB (Network Load Balancing) for CAS and HUB for high availability http://blogs.msdn.com/b/douggowans/archive/2008/12/08/nlb-and-the-cas-hub-role.aspx 2. What licnese should i purchase (standard or enterprice) ? Hub Transport does not require Enterprise Edition of Windows Server 2008 for high availability. This clustering functionality if built into both Exchange 2010 standard and enterprise edition. Client Access does not require Enterprise Edition of Windows Server 2008 for high availability. To cluster a Client Access Server Array you need to implement NLB (Network Load Balancing). However if you have a third-party hardware-based network load-balancing for stateless applications such as a CAS server, you can get away from using Network Load Balancing. Remember when planning for NLB implementation it is best to create a separate VLAN for NLB cluster traffic. Network Load Balancing is a feature of Windows Server 2008 Standard and Enterprise. http://clintboessen.blogspot.com/2010/01/exchange-2010-licensing-and-high.html 3. if build up redundancy(not cluster) , should i need to have 2 CAS and 2hub transport server or only 2 x server install both CAS and hub transport? I would recommend you to use Hardware load balancer from Performace point of view. Thanks Mhussain

Hello You can do NLB (Network Load Balancing) for CAS and HUB for high availability http://blogs.msdn.com/b/douggowans/archive/2008/12/08/nlb-and-the-cas-hub-role.aspx 2. What licnese should i purchase (standard or enterprice) ? Hub Transport does not require Enterprise Edition of Windows Server 2008 for high availability. This clustering functionality if built into both Exchange 2010 standard and enterprise edition. Client Access does not require Enterprise Edition of Windows Server 2008 for high availability. To cluster a Client Access Server Array you need to implement NLB (Network Load Balancing). However if you have a third-party hardware-based network load-balancing for stateless applications such as a CAS server, you can get away from using Network Load Balancing. Remember when planning for NLB implementation it is best to create a separate VLAN for NLB cluster traffic. Network Load Balancing is a feature of Windows Server 2008 Standard and Enterprise. http://clintboessen.blogspot.com/2010/01/exchange-2010-licensing-and-high.html 3. if build up redundancy(not cluster) , should i need to have 2 CAS and 2hub transport server or only 2 x server install both CAS and hub transport? I would recommend you to use Hardware load balancer from Performace point of view. Thanks Mhussain Thanks Mhussain, On answer of question3, is it means that both CAS and HUB can installed in the same server and create other server for load balancer? thank you very much