Performance problems after MS KB4054856 .Net Framework 4.7.1

[stewsie]

In March I had to open a support call as performance of the Veeam service was very slow in particular copy and tape jobs. After some investigations by me two security patches were uninstalled and performance has been back to usual levels. Two weeks ago one of the uninstalled patches was reinstalled with no degradation of service.

The second one was installed yesterday KB4054856 and again the performance issue appears to have returned.

Has anyone else experienced performance problems after installing this patch?

Diskpsd results for one of the repositories is as low as 1.12 MB/s hence the very poor performance. I have not opened another support call as I do not see the point of doing this.

[DonZoomik]

A really long shot, but occasionally .Net patches require recompiling system library assemblies. Windows usually does it by itself (async or when assembly is required) but occasionally i've seen it need a push as it doesn't recompile and uses slower JIT version. If system is using non-compiled assemblies, any application using .Net (C#, PowerShell...) is slower.

From administrative command line run:
cd %systemroot%\microsoft.net&&for /r %a in (*ngen.exe) do %a update
If you want to be extra agressive, you can append /force flag to force recompiling all assemblies. However this oneliner will then recompile all assemblies twice if you have both .Net 3.5 and 4+ installed. Call ngen directly once for each architecture to avoid that.

It usually spits out a ton of warnings that some assemblies cannot be compiled, that's normal. However if you see some libraries being compiled, this could be your issue. Restart Veeam services/proceses after that so it would load compiled assemblies.
As I said, it's unlikely to be your source issue as Diskspd is C/C++ (thus not explaining the slowdown), however Veeams runs on .Net so it might help a bit.

[stewsie]

Thanks for the info. I will review and see what happens.

First thing I am going to do is to reboot the server again once the running jobs finally finish. What is really strange is that backup performance is not affected at all. Only cope and tape jobs. Tape jobs are using the copy files.