This is a different case. The original report used "qemu-img create" in step 2, which results in a sparse image that refers to the backing file for all data. Your sequence has "qemu-img convert" instead, which fully populates disk.qcow. Therefore, in step 3, "qemu-img convert" leaves the full allocation intact.
-- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/660366 Title: "qemu-img convert -O qcow2 -o backing_file" makes huge images Status in QEMU: Fix Released Bug description: $ dd if=/dev/urandom bs=1M of=1.img count=4 4+0 records in 4+0 records out 4194304 bytes (4,2 MB) copied, 1,0413 s, 4,0 MB/s $ qemu-img create -f qcow2 -b 1.img 2.img Formatting '2.img', fmt=qcow2 size=4194304 backing_file='1.img' encryption=off cluster_size=0 $ qemu-img convert -O qcow2 -o backing_file=1.img 2.img 3.img $ du -h ?.img 4,1M 1.img 144K 2.img 4,3M 3.img The conversion result is bigger then the source! It appears that "-o backing_file" is not applied to data (as expected). I.e. all data is put into the resulting image: both from source image and "backing" image. Expected behavior is to put only data that is not present in backing_file. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/660366/+subscriptions
