KVM qcow2 drive falloc or metadata for server on SSD?

Question

Virtualization

I heard/read somewhere that the qcow2 disk created by metadata gives a performance decrease when it is filled with data at values ​​close to the maximum. Or reducing the free space of the host system itself with virtual machines. Something like fragmentation, which is not visible, but strongly felt.

For SSD, fragmentation does not seem to exist. What performance of the disk system in some conventional units will be in comparison if

1. Use a server with an SSD without a virtual machine
   
2. Create virtual machine with metadata disk image
   
3. Create a virtual machine with a falloc disk image