SQL Server 2008 SP installation

I have installed SQL Server 2008 SP2 on some Windows Server 2008 servers, and have some notes about the process.
When I started the version of SQL Server was „10.0.2531.0“, and after the installation the version is „10.0.4000“. This is also what is reported through SMO.

This update has been done in a database mirroring setup, where the principal database instance was update and restarted first. No action was taken to keep the database mirrors running.
After each update and restart the database mirrors came up by themselves.

The installation checks for files in use and reports that the file „fdhost.exe“ is in use and not controlled by the update wizard. This file is used by the Full-Text Search feature. To get a clean check I stopped the service „SQL Full-text Filter Daemon Launcher“ and end the process „fdhost.exe“ on each database instance.

When the installation is completed, the log files and other files from the process are placed in the folder "%ProgramFiles%\Microsoft SQL Server\100\Setup Bootstrap\Log\{time stamp: YYYYMMDD_hhmmss}". The file "Summary_{database instance name and time stamp}.txt" is the most interesting as a start.
Also the Error Log contains a lot about the update.

On one occasion the update failed with a message about „One or more files do not match the primary file of the database. If you are attempting to attach a database, retry the operation with the correct files.  If this is an existing database, the file may be corrupted and should be restored from a backup.“.
The service for the database instance could not start, and the same error message was given each time.
In the file "Detail.txt" there is a exception "Microsoft.SqlServer.Chainer.Infrastructure.ChainerInvalidOperationException" and it looks like some write operations to the Registry failed.
A restart of the computer made the update to finish correct and the database to start. Now with the updated version number.

Even though services was stopped and processes was ended you are prompted to restart the computer. In the Summary log file there are several entries about a restart is required. I did restart the computer to comply.

Reference

SQL Server Team Blog: „SQL Server 2008 SP2 is available for download today!“.
KB2285068: „List of the bugs that are fixed in SQL Server 2008 Service Pack 2“
Microsoft TechNet Library: „Full-Text Search Architecture“.