ZFS VHDX Growing on Hyper-V 2019

I fiddle about with a charming little PFSense firewall at home, which I recently managed to mangle, so I decided to rebuild it on my new Windows Server 2019 Hyper-V virtualization host. Excitement!

Having thought that at least some of my problems were to do with file corruption, I did some very, very basic research, and decided this new-fangled ZFS thing sounds like the way to go!

It was great until it wasn’t! Here’s a snapshot of my drive size over time:

02/02/2019  08:27 PM     5,674,893,312 PFSense2019ZFS.vhdx
03/02/2019 02:21 PM 7,923,040,256 PFSense2019ZFS.vhdx
03/02/2019 02:30 PM 7,956,594,688 PFSense2019ZFS.vhdx
03/02/2019 02:51 PM 8,090,812,416 PFSense2019ZFS.vhdx
03/02/2019 02:52 PM 8,090,812,416 PFSense2019ZFS.vhdx
03/02/2019 02:52 PM 8,090,812,416 PFSense2019ZFS.vhdx
04/02/2019 03:19 PM 11,244,929,024 PFSense2019ZFS.vhdx
04/02/2019 03:29 PM 11,244,929,024 PFSense2019ZFS.vhdx
04/02/2019 03:59 PM 11,312,037,888 PFSense2019ZFS.vhdx
18/02/2019 03:14 PM 57,248,055,296 PFSense2019ZFS.vhdx
19/02/2019 05:40 PM 60,536,389,632 PFSense2019ZFS.vhdx

So over about 2 weeks, I’d used ~60GB of space(!) Unfortunately the drive size available on this host is only 120GB, so I’m already unable to export a copy locally. Grumble.

So I’m unsure what the moral of the story is. Sorry about that, I was hoping for a stronger conclusion too!

Does ZFS not work nicely with VHDX expanding disks? Does PFSense 2.4.4. chew disk space that it doesn’t report within the OS itself? Can I squeeze another question in before returning to my drive-switch-a-roo export and rebuild?