qemu-img create with extended_l2=on, followed by virt-install

Hi! I have read the following blog post: https://blogs.igalia.com/berto/2020/12/03/subcluster-allocation-for-qcow2... and watched the video displayed there. 1) To make qcow2 as fast as possible, does it make sense to do the following: [#] qemu-img create -f qcow2 -o extended_l2=on,cluster_size=128k my_image.qcow2 1000GB And then: [#] virt-install —name=MyVM --disk path=my_image.qcow2,size=1000 . . . Will this overwrite the qcow2 file already created or will it keep its characteristics? Does it make sense? 2) I wont’t be moving the VM around much and have the space I need, so I wonder if it will be faster to do the following: [#] qemu-img create -o preallocation=full -f qcow2 my_image.qcow2 1000GB And then: [#] ] virt-install —name=MyVM --disk path=my_image.qcow2,size=1000,bus=scsi,sparse=false . . . (Running bus=scsi so I can trim the image ). I could use a dedicated disk for the VM instead of using qcow2, but I like the flexibility of qcow2. Thanks a lot for any information about this! :-) Best regards, Richard Taubo