qcow2 snapshot on newly created files are fast: # qemu-img create -f qcow2 test.img 200G # time qemu-img snapshot -c snap1 test.img real 0m0.014s
but if metadata is allocated it gets very slow: # qemu-img create -f qcow2 -o "preallocation=metadata" test.img 200G # time qemu-img snapshot -c snap1 test.img real 1m20.399s but reading the metadata is also fast: # time qemu-img check test.img real 0m0.371s So why is creating a new snapshot that slow - any ideas?
