At times, you will be forced to reboot your exchange server, either after installing certain security patches or when the server is taken down for maintenance.
If you are a small shop and run your exchange on the domain controller, you will find that it takes more than five minutes for the server to stop all the services (evident if the server is 2008) and reboot. I am not talking about the overall time it takes for the server to reboot and come back online fully operational, but the time it takes for the server to go into a reboot mode.
So why does it take too long for the server to reboot, you would think. The answer is that the active directory services stop much before the exchange ones and exchange needs to talk to the domain controller while stopping its services. This mismatch forces exchange services to wait and timeout trying to talk to the domain controller before the server can reboot.
So, what can be done to reduce the server reboot time?
I would suggest to stop the following exchange services before you restart your server.
Exchange AD Topology Service, Exchange Information Store and Exchange System Attendant. Stopping AD Topology Service will automatically stop all other related exchange services.