With Exchange 2010 comes many advantages in the HA realm. One of them is the ability to connect to the Client Access Server for RPC. This means, when a Mailbox Server does a *over (failover or a switchover), the user is still connected to their RPC Endpoint. You can also create a Client Access Array which load balances your RPC Endpoint on your CAS Servers. Lots of information on the RPC Client Access Server here and here. So what options are available for load balancing this new RPC Client Access Array and at the same time, load balancing all our other services? And what are the pros/cons of each method? If you want to know, read on…
Exchange Load Balancing Options
In Exchange 2007, if you wanted any type of HA, you needed at least four servers. 2 for CCR Nodes and 2 for HUB/CAS Nodes. The reason why you cannot have 2 nodes altogether is that CCR Nodes were limited to the Mailbox role only. For an Exchange Site, you need to always have at least the HUB/CAS/MBX Role for that site to be operational. In Exchange 2010, this was fixed. You now have something called Database Availability Groups (DAGs). These DAG members can contain all Exchange roles (HUB/CAS/MBX/UM) but still may not contain the Edge Transport role.
There is a problem though. There is a Windows limitation that allows you to install Windows Network Load Balancing on a server that also contains Failover Clustering Services. So while we can now have 2 Exchange 2010 Servers, we need a way to load balance the CAS role to provide High Availability for the following CAS Services:
--> The rest is on the blog : http://www.shudnow.net/2010/03/17/exchange-2010-rtm-high-availability-load-balancing-options/