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The information about a COW image and its reference are obtained through “info” of the image utility “qemu-img” that is passed to the “backing-chain”: ~/vbox/kvm $ qemu-img info -backing-chain img01.qcow2 rw- 1 anis users 486M Jun 9 14:29 vm01.qcow2 Information about COW pictures ~/vbox/kvm $ qemu-system-x86_64 img03.qcow2 &īut their volumes represent just the difference between the original disk and the current status: The “differential” images can be used simultaneously: ~/vbox/kvm $ qemu-system-x86_64 img01.qcow2 & Note: To ensure the preservation of the original image, it can be protected on written by a “chmod aw vm01.qcow2”. ~/vbox/kvm $ qemu-img create -f qcow2 -b vm01.qcow2 img03.qcow2įormatting 'img03.qcow2', fmt=qcow2 size=8589934592 backing_file='vm01.qcow2' encryption=off cluster_size=65536 lazy_refcounts=off ~/vbox/kvm $ qemu-img create -f qcow2 -b vm01.qcow2 img02.qcow2įormatting 'img02.qcow2', fmt=qcow2 size=8589934592 backing_file='vm01.qcow2' encryption=off cluster_size=65536 lazy_refcounts=off The needed image COW can be generated with the same reference. The created image is smaller than the reference image (193K for a reference about 486M) because during the creation there is no difference between the original and the COW. So they go through the utility “qemu-img” in “create” which passed on the disc format (“-f Format”) and the reference image (option “-b reference image”): ~/vbox/kvm $ qemu-img create -f qcow2 -b vm01.qcow2 img01.qcow2įormatting 'img01.qcow2', fmt=qcow2 size=8589934592 backing_file='vm01.qcow2' encryption=off cluster_size=65536 lazy_refcounts=off The generations of COW images are simple created images. Note:The activation of compression about the transition from vmdk format to qcow2 format via the “-c” of “qemu-img” which, in this case reduces by more than 50% the size of the virtual machine. ~/vbox/kvm $ qemu-img convert -c -O qcow2 ~/vbox/vm/vm.vmdk vm01.qcow2 rw- 1 anis users 1.1G May 28 10:58 /users/anis/vbox/vm/vm.vmdk