When applying CU10 HF1 (August 2019) to a Skype for Business Server 2015 Standard Edition Server running CU3 (November 2016), Server.msp failed to install with the following error.
Checking service status. This may take a couple of minutes…
Installing 1 of 1 Updates for [Skype for Business Server 2015 6.0.9319.562]
Installing KB4518735 for Server.msp
ERROR 1603: Server.msp had errors installing.
All other updates installed successfully.
With no clues from the installer logs, I ran the Skype for Business Server 2015 Deployment Wizard.
Step 2: Setup or Remove Skype for Business Server Components.
Click Run Again.
Step 2 failed with the following error and a major clue.
Command execution failed: Install-CsDatabase was unable to find suitable drives for storing the database files. This is often due to insufficient disk space; typically you should have at least 32 GB of free space before attempting to create databases. However, there are other possible reasons why this command could have failed. For more information, see http://go.microsoft.com/fwlink/?LinkId=511023
There must be a minimum of 32GB free disk space on the C: drive to install the Server.msp update. Free up space or extend the volume.
On this particular server the Skype for Business 2015 install is all on the C: drive.
But what if the databases had been on a non-OS disk where there was sufficient free disk space?
Run the CU Installer, Server.msp will fail.
Run the following PowerShell command in Skype for Business Server Management Shell to update the databases, specifying the correct path.
Install-CsDatabase -LocalDatabases -DatabasePaths [PATH] -Update
Install-CsDatabase -LocalDatabases -DatabasePaths D:\CsData -Update
Re-run the CU Installer, Server.msp should install successfully.