Thanks for the fast reply guys. 

I raised a Bug report for the other issue: https://bugzilla.redhat.com/show_bug.cgi?id=1729292


Am 11.07.2019 um 18:08 schrieb Ján Tomko <jtomko@redhat.com>:

On Thu, Jul 11, 2019 at 05:19:03PM +0200, Peter Krempa wrote:
On Thu, Jul 11, 2019 at 16:46:29 +0200, Julian Sternberg wrote:

[...]

Seconds strange behavior is as follow:
virsh vol-create-as vm_volumes test.img --capacity 1G --format raw
error: Failed to create vol test.img error: unsupported configuration: only RAW volumes are supported by this storage pool

So this is really weird. The error message is produced if the target
format is not 'raw' but the above command clearly supplies it.

I'd suggest you collect debug logs while trying both and attach them
here. Unfortunately I don't see what could be wrong here.

This is a known bug waiting to be fixed:
https://bugzilla.redhat.com/show_bug.cgi?id=1724065

Jano