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What sort of changes are made to System tables (master / model / msdb) by Cumulative Updates? For context, I have SQL servers that have AlwaysOn Groups, and am looking at a way to roll back updates if it causes issues. All data and log files are on dedicated volumes, and SQL is installed on the OS drive.

I have been testing a rollback process where I take a snapshot of the OS volume before installing the CU, and then update. After updating, I am able to restore the OS snapshot image back, and SQL shows the pre-update patch version. It looks like everything is working as expected after the rollback (i.e. the program files / DLLs / registry are all reverted), and not seeing any errors, but not sure if I am missing something or there is something that i should be aware of that might break something or be a risk.

Thanks in advance.

SQL Server version 2017 (im testing this is an old environment i had set up somewhere), and have tested this on a CU22 -> CU31 update + rollback.

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What sort of changes are made to System tables (master / model / msdb) by Cumulative Updates? For context, I have SQL servers that have AlwaysOn Groups, and am looking at a way to roll back updates if it causes issues.

Assuming Microsoft did their job correctly, this will be handled by the installer when configuring the install or the uninstall. There shouldn't be anything that needs to be manually executed.

DMVs, XEs, etc., are all taken care of by the resource database which is replaced by the installer and will be reverted to the previous version if uninstalled.

I have been testing a rollback process where I take a snapshot of the OS volume before installing the CU, and then update.

I wouldn't do this. Depending on where everything is installed, files may be changed not on an OS volume. If any databases sit on that OS volume, there is a chance of database corruption from in-flight transactions. YMMV until the one day you run into an issue.

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  • The database files are all on dedicated volumes (user databases and system ones like master / model / msdb). But for rollback process of CU patching, recommend using uninstall over snapshot + revert (of OS / program file volume) - thanks for the info.
    – Brett
    Commented Mar 18 at 18:00

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