Install Exchange 2010 SP3

In my test environment I have configured a server with Client Access and Hub Transport server role and two mailbox server as database availability group (DAG).

Download Exchange Server 2010 Service Pack 3

The recommended order for the upgrade is as follows:

Client Access
Hub Transport
Unified Messaging
Mailbox

Since the servers are monitored by SCOM 2012, I put all servers into maintenance mode and stopped System Center Management Service (SCOM Health service).

An upgrade can be performed through (using) GUI, starting setup.exe or when being in unattended mode through command. 
Here is the upgrade of CAS/HUB Server through command:

SETUP /m:upgrade /InstallWindowsComponents

With Get-ExchangeServer | fl Name,AdminDisplayVersion you can check the version.

Upgrade Mailbox Servers in DAG

Since Exchange 2010 SP1, there are some new functions and scripts. Amongst others "StartDagServerMaintenance.ps1" and "StopDagServerMaintenance.ps1". Both scripts were created for maintenance of group members of a DAG.

StartDagServerMaintenance.ps1 and StopDagServerMaintenance.ps1(new)   You can use StartDagServerMaintenance.ps1 to take a DAG member out of service for maintenance. It will move active databases off of the server and block databases from moving to that server. It will also make sure all critical DAG support functionality (for example, the Primary Active Manager PAM role) that might be on the server is moved to another server, and blocked from moving back to the server. Another script, StopDagServerMaintenance.ps1, is provided to complete the operation and remove the blocks.

Detailed description:
  

New High Availability and Site Resilience Functionality in Echange 2010 SP1

German Version  

Status of the Database:

Scripts are located at:  \Program Files\Microsoft\Exchange Server\V14\Scripts

After that run script from  .\StartDagServerMaintenance -ServerName LABMXDAG02  Cluster Node 2 is set to pause.

Mailbox Databases are moved to Node 1:

Even with Get-MailboxDatabaseCopyStatus * check if everything fits.

Now, the upgrade can be started here as unattended setup:

Setup.com /M:Upgrade /InstallWindowsComponents

Now the maintenance mode will be terminated:

.\StopDagServerMaintenance -ServerName LABMXDAG02

The mailbox databases remain active on the Node 1.

Next, the second DAG member server is updated analogously. 

You can run the script RedistributeActiveDatabases.ps1 for distribution of databases based on configured preference.

.\RedistributeActiveDatabases.ps1 –DagName DAG01 –BalanceDBsByActivationPreference –Confirm:$false

Then checking the version:

Get-ExchangeServer | fl Name,AdminDisplayVersion

Done.