I have read in a number of blog posts & forums that you can have a resilient & redundant 2010 messaging system with just two servers, making use of the new DAG functionality and the option to install CAS & HUB roles on the DAG members as well. This becomes a big driving factor for people to upgrade from 2007, which needs atleast four servers to provide a redundant solution.
Though this is true, certain points need to be considered.
- You can install CAS & HUB roles on both DAG members
- But you cannot have them load balanced using NLB, as you cannot have both clustering and NLB running on the same servers.
- An external load balancer (not ISA server) becomes the option to configure a load balanced CAS array with just two servers.
- Once you have a load balancer, CAS array needs to be configured on all mailbox databases.
Many are not aware of this fact & hence thought of making it clear.