[nmglug] QEMU/KVM; Thunar as root?

[Tom Ashcraft]

I've got Debian 10 XFCE installed to and running from a USB stick.  
Inside that I have two identical Debian minimal-install server VMs that 
run under QEMU/KVM behind NAT so that I can have the two talk to each 
other as a network inside the single computer.  This for purposes of 
safely practicing and experimenting with things like SSH keys and 
WireGuard without external network or internet access.  All, well and 
good; works great as long as I stick to the same computer and nic with 
which I created the VMs.

The problem is that I have limited storage for snapshots and clones so 
that currently, if I screw something up or switch computers, experience 
indicates that I have to create new individual VMs by installing from 
scratch to start again clean. That takes a long time.

So I'm thinking that before I waste too much more time reinventing the 
wheel every time I go 'round, that I ought to be able to copy clean 
unused images of my two VMs on another USB stick so that I can just 
conveniently delete and replace as required.

First question:  I ought to be able to create an elastically sized VM 
with QEMU/KVM in a manner similar to how dynamically allocated storage 
works in VirtualBox so that the image I copy across different USB sticks 
can be relatively small and quick to copy?

Second question:  At present I must copy via command line as root or 
with sudo as Thunar GUI file manager won't give me permission by any 
means I can discover.  I'd like to use Thunar so I can get some visual 
feedback about copy progress.  I ought to be able to run Thunar from the 
desktop as root somehow, right?

As I write I *think* my old laptop with USB 2.0 is somewhere in the 
midst of copying an 8.0 GB image, but it keeps timing-out into 
lockscreen, and for all I know something has gone wrong.  The USB sticks 
are warm as a cup of coffee, but the cursor in the terminal is just 
sitting there without blinking and it's all taking way too long:

tom at debian10xfceUSB: /var/lib/libvirt/images$ sudo cp generic-2.qcow2 
/media/tom/C58A-66EE/

All hints and advice are welcome.

Thanks,

Tom