Hi All 

I am planning to upgrade my exchange server 2013 SP1CU4 to CU7 . As per my understanding , we always proceed with the CAS servers and then the Mailbox Servers during up-gradation.

But I am confused now , since I have seen articles stating , that the Mailbox servers has to be upgraded first and then the CAS servers in exchange 2013. 

What will be the correct order . My environment consists of 2 Mailbox servers in DAG and 2 CAS servers (Exchange server 2013 SP1)

Thanks in Adv

Hi Joyso,

The Microsoft recommendation regarding the order in which the Exchange 2013 server roles should be installed or Upgraded is Mailbox and then CAS.

It makes sense as the CAS Role is a stateless server and all major components are held by the Mailbox Role.

Until a 2013 mailbox server comes online, the CAS server is pretty much useless. Hence, the recommended installation order in 2013 is the reverse of 2010 Mailbox role first & then CAS

Note: If your DAG have more nodes, you need first upgrade all non-PAM nodes and then upgrade PAM node.

Some References:

• The recommendation from the Product Group is to install Exchange 2013 Preview Mailbox Role first, and then the CAS role.
• If you're separating your server roles, we recommend installing the Mailbox server role first.
  
• Upgrade your Exchange 2013 server roles in the required order. First, upgrade Mailbox servers and then upgrade Client Access servers. -Upgrade DAG Mailbox servers
  
• Exchange 2013 Server Roles Installation Order Mailbox First:
  

"Note: If your DAG have more nodes, you need first upgrade all non-PAM nodes and then upgrade PAM node."

No need to worry about which server holds the PAM node. It can moved to any server in the DAG at any time. When you put the server in maint mode, that process is usually when the Quorum is moved. If not, a reboot will move it.