We currently have a single Windows 2003 server install for Exchange 2003. We use a separate ISA 2004 box on the perimeter for the SMTP host. I need some assistance or advice/recommendation on which direction to go for our upgrade to Exchange 2007. We have approximately 300-400 mailboxes, divided over 3 different mailstores. We are licensed for the Enterprise Edition.
Initial reading led me to think I would try the CCR flavor with 2 clustered Server 2008 boxes and continue to use ISA on the perimeter in place of an Edge server role, however I just recently discovered that if using clustering that the clustered boxes can only have the mailbox role installed, therefore I would then need at least 1 more server to contain the CAS and HUB roles. Now I'm looking at 4 servers total involved in messaging and the only redundancy is on the actual database server.
I need some advice here. If I don't cluster the mailbox server and install the mailbox, cas and hub roles all on the same box what type of fail safe measure can I implement? Can I still get some redundancy out of this setup? There is just so much literature out there for Ex2007 I'm getting overwhelmed reading all of these different scenarious.