Hello,We have a Windows 2003 domain with Windows 2008 addiitonal domain controllers and Exchange 2003 in a frontend-backend topology. Backend servers are clustered and frontend servers are load balanced with NLB.I am planning to introduce Exchange 2007 into this setup and I have some queries.1. My plan is to start install HT role first and then CAS role? Both HT and CAS roles run on two servers load balanced with NLB. Is it a right install approach for roles in a mixed environment like us? 2. I plan to load balance CAS with NLB and HT will be installed on both servers with no load balancing. I read HT doesn't require load balancing. Is it right?3. I plan to use Windows 2008 R2 for MBX server (clusters) and Windows 2008 standard for CAS/HT roles. Will this be an issue as we use different flavours of Windows 2008 install base? is it recommended?Thanks in advance.

Hi, Client Access, Hub Transport, Mailbox and Unified Messaging. Edge transport can be installed separately from the migration planning, either before, during, or after the other Exchange 2007 server roles. Since we have exchange 2003 servers, I recommend you to install CAS separately from Mailbox Server. After replacing Exchange 2003 front-end with Exchange 2007 Client Access server, an Exchange 2003 mailbox user still can use OWA to access their mailbox through the Exchange 2007 CAS server's /Exchange virtual directory (for example: http://<server FQDN>/Exchange). Thinking about how to replace exchange 2003 front-end server. We cannot install CAS in DMZ, we need to install CAS internally, so we need to publish CAS server(via ISA server or expose CAS server to the internet. ) We can configure NLB for CAS to load balance. By default, connections to Hub Transport servers are automatically load balanced if more than one Hub Transport server is deployed in an Active Directory site. For the operation system, I recommend you apply the latest update for OS and then install Exchange roles. Both nodes in the cluster must have the Windows Server 2008 Enterprise operating system or the Windows Server 2003 Enterprise Edition operating system installed on each node of the cluster using the same boot and system drive letter. Planning for Cluster Continuous Replication http://technet.microsoft.com/en-us/library/bb123996(EXCHG.80).aspx Deployment Options for Hub Transport Servers http://technet.microsoft.com/en-us/library/bb124398(EXCHG.80).aspx Overview of the Network Load Balancing Deployment Process http://technet.microsoft.com/en-us/library/cc771700(WS.10).aspx Load Balancing Exchange 2007 Client Access Servers using Windows Network Load-Balancing Technology – Part 2: Configuring the Windows NLB Cluster http://www.msexchange.org/articles_tutorials/exchange-server-2007/high-availability-recovery/load-balancing-exchange-2007-client-access-servers-windows-network-technology-part2.html Regards, Xiu

Thanks very much for your reply.My design is to have CAS and HT roles running on two W2K8 x64 standard machines and just MBX roles on two W2K8 R2 x64 standard machines. Does having W2K8 install base for CAS and HT cause issues as MBX is running W2K8 R2 install base?TIA

Hi,Please note: The Standard Edition doesn't support the features needed for DAGs. You can't upgrade Windows when Exchange is installed on the server.I think that could be the only thing we need to aware of.So far, we do not have any known issue about different OS for Exchange server roles.Regards,Xiu