In my previous post here, I was referring to the high availability features in built with Exchange 2007. This got matured over last year as Exchange hosting providers were keen on start offering to the customers. There is always a show stopper though! SP1 was not released at that time...Now with the release of SP1, hosters are excited and can't wait any more longer. Yes, its in the offering list of hosting providers. You may want to check out the hosting directory here.
As a customer, you may not go in depth in terms of infrastructure requirements, efforts to build this high available solutions, technical expertise etc..Its all taken care by Hosting providers. However, its better to know underlying principles of HA and what type the hosting providers would be offering to you.
Lets get into the CCR (Cluster Continuous Replication) option. Active/Passive - Only one server in the cluster can service users simultaneously. If active node fails, passive node begin to service clients. This is transparent to the end users.
Note that Active/Active clustering is not supported in CCR. Clustering advantages are beyond faster disaster recovery. For example, if you want to shutdown the mailbox server (active node) for emergency maintenance/patch management, you could just fail the active mailbox node to the passive one, then perform the maintenance/patch management on the active node without interrupting exchange services.
Unlike earlier clustering scenario, the two nodes in a CCR do not have to be identical. We can have different specification in each for the two nodes. This will offer an opportunity for flexibility in using qualified servers in the CCR environment as passive nodes - drastic cost saving for both customer and hosting providers. Having mentioned this option, it is customers & hosting providers responsibility to ensure the performance is not sacrificed and SLA is not affected.