So I'm getting ready to apply the update. I wanted to double check with anyone here who has done the update from SP1 to CU9. Are there any issues I should keep an eye out for? Is the application of the update actually seamless? I found a tutorial on Exchange Server Pro: http://exchangeserverpro.com/exchange-2013-installing-cumulative-updates/ 

Is that tutorial still valid even though it's been a couple years? 

Due to AD schema changes in the other CU's should I worry that my Domain and Forest Functional Levels are still set at Server 2003?

Thanks,

 

The Domain and FFL levels are supported per:

https://technet.microsoft.com/en-us/library/Ff728623%28v=EXCHG.150%29.aspx?f=255&MSPPError=-2147217396

No one can guarantee it will be seamless. But its time to upgrade  :) 

Ensure any 3rd party apps  are supported with Exchange 2013 CU9.

A human error occurred during installation of CU9 one of our DAG servers. The server was configured with exchange installed on a different hard drive and the during the installation the tech didn't select the option in order to change the installation directory. Other than completely removing the server from the DAG, and uninstalling Exchange 2013 is there anyway to fix this mistake?