Hyper-V and OpnSense: Volume Shadow Copy Causing VM Issues

[iorx]

Hi!

I'm experiencing an issue with FreeBSD 14.2 and OPNsense as a guest in Hyper-V, specifically related to the Integration Service Backup (Volume Shadow Copy).

Before posting this on a FreeBSD-specific forum (thinking forums.freebsd.org...), I wanted to check if anyone here has a working OPNsense/FreeBSD setup (any version) with functional integration of the Shadow Copy Service in Hyper-V.

The symptoms are:

• If the Integration Services Backup (Volume Shadow Copy) is enabled, restarting or shutting down the host (Hyper-V) causes the OPNsense VM to get stuck.
• This prevents the server from performing a clean shutdown of ALL VMs.
• After a while, Hyper-V forcibly kills ("pulls the plug") on ALL VMs and then reboots/shuts down.

Workarounds:

• Manually stop OPNsense before rebooting the host.
• Disable the "Backup (Volume Shadow Copy)" integrated service for the OPNsense VM.
• In all my OPNsense installations, I have to disable this integration service to maintain a functional Hyper-V environment.

Question:

Does anyone know if this behavior is "by design" or if there's a fix that can be applied to OPNsense/FreeBSD?

I've encountered this problem from Windows Server 2016 through to 2025. The same issue persists across different versions of FreeBSD/OPNsense.

My own research hasn't yielded any solutions or even a discussion on the subject.

Best regards!
(edit, changed OpnSense into OPNsense ... 😁)

[sits]

Hey irox

In a newer OPNsense installation, I'm also struggling with VSS not working on Hyper-V.

After a long search, I found out that hv_vss apparently ONLY works with UFS:

hv_vss only support UFS currently. If any of file system Partition is non UFS, the VSS capability check will fail.

Source: https://man.freebsd.org/cgi/man.cgi?query=hv_vss&sektion=4&apropos=0&manpath=FreeBSD+14.0-RELEASE+and+Ports

I've installed OPNsense on ZFS so that could be the problem (at least in my case).
I'll give it a try with UFS ASAP and report here (if I don't forget to).

Best regards!
Christian