How to apply windows service pack and exchange servive packs?
Here is a brief instruction on how to install service packs or security patches on cluster enviroment.
1. Apply patches to the front end servers first. (In this lab they are exfe01 and exfe02, one at a time)
2. Apply patches to the current passive node (if exbe01 is active, exbe02 is passive, apply patch to exbe02)(You might have to stop "cluster" service on passive nodes).
3. Fail over exchange servers to passive node. (now exbe02 is active and exbe01 is passive)
4. Apply patches to the current passive back end servers. (exbe01)
5. You may can move exchange servers to original active node(make exbe01 as active node and exbe02 as a passive node) -> that is an extra downtime for users.
* You also want to follow the same procedure if you want to apply BIOS updates, driver updates and so on.