On the internet I found this nice visual that helps understanding the Hyper-V and Backup Infrastructure.
After we installed a Hyper-V on a new Window Server 2019, everything seemed to be running OK.
But apparently after the 1st backup there where a lot of errors in the Event viewer ID 19100.
After that point no backups would run anymore, until the Hyper-V host was restarted.
Next backup cycle the same story
So I checked the VSS writer to see if all was OK. But I saw that there was an error reported?
Microsoft Hyper-V VSS writer : Unexpected Error ?
So that did not help a lot ?
Next I ran some VSS diagnostics apps, but no errors found ?
Everything pointed out to be OK, but it was not …
Conclusion was that this could be nothing else then a Permission issue.
So I ran the Resultant Set of Policy – rsop.msc
I noticed that some policies where overruled by a Domain Policy so I started cleaning up.
But still no success until I noticed that the Local Log on As a Service Policy again I clean this one up.
And check the local Policy settings for this policy using SecPol.msc
I noticed that the ‘NT VIRTUAL MACHINE\Virtual Machines’ was not in there ?
After adding the NT VIRTUAL MACHINE\Virtual Machines to the LOCAL Policy ‘Allow run as a Service’
All Backup problems were solved.
Make sure the Hyper-V Guest Integration Services and the Backup (Volums Shadow Copy) are active as well
And the CheckPoints are set like this