UPDATE 11/08/2020
Sparky 2020.09 (UEFI mode) rolled forward all the way through up to the time of writing behaves same way on bare metal .
END UPDATE
Due to Libvirt version 6.8.0 there is no more any problems with deployment KVM Guests on EXT4 file system, compare with http://lxer.com/module/newswire/view/290245/index.html
Deploy SparkyLinux 2020.9 ( rolled forward up to 11/08/2020 ) as KVM guest on F33 Server as follows
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VM has been deployed in legal BIOS mode on EXT4 filesystems
Issue with Btrfs in Libvirt 6.6.0 has been fixed in Libvirt 6.7.0 release.
Bug fixes : Fix logic in setting COW flag on btrfs
When COW is not explicitly requested to be disabled or enabled, then libvirt should do nothing on non-BTRFS file systems.
See for details http://lxer.com/module/forums/t/36708/
There is no any more any problems with deployment KVM L2 Guests on EXT4 FS
Install KVM
$ sudo apt install qemu-kvm libvirt-daemon bridge-utils \
virtinst libvirt-daemon-system -y
$ sudo apt install libguestfs-tools libosinfo-bin \
qemu-system virt-manager -y
$ sudo modprobe vhost_net
$ lsmod | grep vhost
$ echo vhost_net | sudo tee -a /etc/modules
$ sudo reboot
Install Web Cockpit Console
$ sudo apt install install cockpit cockpit-machines
$ sudo apt install cockpit cockpit-machines
$ sudo systemctl start cockpit.socket
$ sudo systemctl enable cockpit.socket
Tuning firewall
$ sudo apt install firewalld
$ sudo firewall-cmd --add-service=cockpit --permanent
$ sudo firewall-cmd --reload