Hello all

We  currently have 2 DAG's, 5 nodes in each DAG. We also have 8 CA servers, 4 in each data-center.  Because i have to update 18 servers, i want to know if i can update one datacenter at a time. Example update the Exchange servers in DC1 to CU9, then the next day update the exchange servers in DC2 to CU9. Is this something i can do without running into issues with different versions?

In Exchange 2013, order is to upgrade the internet facing site first and in the site, Mailbox server first and then CAS.

More to detail reference article : http://exchangeserverpro.com/exchange-2013-installing-cumulative-updates/ 

Hi,

Blog for reference: How to Apply Exchange Server 2013 RTM to Cumulative Update 1

http://blogs.technet.com/b/justin_gao/archive/2013/04/09/you-need-to-know-how-to-apply-exchange-server-2013-rtm-to-cumulative-update-1.aspx

Best Regards.