Just playing around with OpenZFS on Catalina. OpenZFS 1.9.3.1, macOS 10.15.2.
Created a zpool on a single external 1 TB disk:
sudo zpool create -m none tank2 disk12
Created a zvol on that:
sudo zfs create -V 880g tank2/foobar
Used macOS Disk Utility to format the zvol foobar with APFS unencrypted. It shows up on the desktop and works just fine, but...
Time machine is excluding this volume (in Time Machine Preferences -> Option), and I cannot un-exclude it. It's gray like TM is saying nuh-uh ain't gonna touch this. Is this a limitation of Time Machine or ZFS? Is there any workaround to enable Time Machine to back up this volume?
Also tried with an HFS+ volume... same problem.