Cumulative Updates (CU) are kind of a service pack that comes out quarterly for Lync Server and the clients. It includes fixes and some times new functionality is added.

The latest is Cumulative Update is CU4 (as of December 2011) and it can be downloaded here http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=11551

As you can see there are a lot of files to download and you could just download and update specific components or you can download the LyncServerUpdateInstaller.exe package that includes all the latest updates. So go ahead and download it and then copy the file to your Lync Servers.

To start the update process log in to your server. And start the Lync Server Management Shell

1. Check that no users are talking on the phone or are in a meeting before you start the update. You can do this by running Get-CsWindowsService (read more in this post http://www.ultimate-communications.com/2011/11/lync-powershell-tip-5/ )
   
1. In the screenshot above there are one active call in the call park service and it would be a bad idea to turn off the services right now as this would terminate the call.
2. So the solution would be to prevent new sessions for a while and drain the active connections. This can be done running Stop-CsWindowsService –Graceful
   (Read more on server draining at http://voipnorm.blogspot.com/2011/03/lync-server-draining.html )
1. 
   As seen in the picture the services is now stopped.
3. Next thing would be to stop the World Wide Web service. By typing: net stop w3svc
4. Now Close all Lync Server Management Shell windows.
5. Install the cumulative update for Lync Server 2010 by running LyncServerUpdateInstaller.exe
   
   This will start the update tool and you should se what updates are needed and what version is already installed. (As you can see in the picture I have already installed the latest update package and it shows a green checkmark at every line. If there were some services that wouldn’t be updated this would show a red stop mark instead.)
1. Restart the computer if you are prompted to do so
6. The next step is something that is almost always forgotten. To update the Lync Server Databases (this step is normally not done if you just used Windows Update to update your Lync server and should then be done manually after Windows Update has updated your server.)
1. Start the Lync Server Management Shell: (Click Start, click All Programs, click Microsoft Lync Server 2010, and then click Lync Server Management Shell.)
2. To apply the changes made by LyncServerUpdateInstaller.exe to the SQL Server databases do one of the following:
1. If Enterprise Edition Back End Server databases are not collocated with any other databases, such as Archiving or Monitoring databases, at the command line, type the following:
   Install-CsDatabase –Update –ConfiguredDatabases –SqlServerFqdn <SQL Server FQDN>
2. If Enterprise Edition Back End Server databases are collocated with other databases, such as Archiving or Monitoring databases, at the command line, type the following:
   Install-CsDatabase –Update –ConfiguredDatabases –SqlServerFqdn <SQL Server FQDN> –ExcludeCollocatedStores
3. For Standard Edition, type the following:
   Install-CsDatabase –Update –LocalDatabases
7. Now when the database is also up to date, its time to start the IIS & Lync Server services. At the command line, type:
   net start w3svc
   Start-CsWindowsService

And that’s it you should now be up to date and ready to roll out the client updates to your Lync clients and phones.

Have I missed something that you considerer being a best practice when updating your server? Please comment bellow.