-- QCOW2 ALLOCATION BREAKDOWN -- Active Data [####################################] 12.1 GB (20%) Orphaned Data [######## ] 3.2 GB (5%) <- Reclaimable! Zero Clusters [ ] 0.1 GB (<1%) Free Space [####################################] 44.6 GB (74%)

virsh snapshot-create-as win7-vm clean-state --disk-only --atomic

QCOW2 is a copy-on-write format. If not configured correctly, it slows down over time.

qemu-img create -f qcow2 win7.qcow2 40G