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[Qemu-devel] [Bug 660366] Re: "qemu-img convert -O qcow2 -o backing_file

From: Ildar
Subject: [Qemu-devel] [Bug 660366] Re: "qemu-img convert -O qcow2 -o backing_file" makes huge images
Date: Thu, 23 May 2013 08:08:12 -0000

** Changed in: qemu
       Status: Confirmed => Fix Released

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  "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

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