[Qemu-discuss] Noop convert in qcow2 removes interal snapshots

[Joseba Martos]

Hello.

I have a qcow2 image with RHEL installed for creating a demo. The image size is 12 GB  but the internal filesystem is using only 11 GB, so this image has 11 GB unused. For shrinking, I'm using "qemu-img convert" from qcow2 to qcow2 (noop) and the images shrinks correctly to 1 GB. This image has a internal snapshot taken with virt-manager. After converting the image, the snapshot is lost. I often use this snapshot capability and I want to know if is any way for shrinking the image without losing the internal snapshots. I tried virt-sparsify too, with the same result, because it internally uses "qemu-img convert".

Lot of thanks.

I attached some technical extra info below:

* Qcow2 image before shrinking:

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$ qemu-img info rhel-7.qcow2
image: rhel-7.qcow2
file format: qcow2
virtual size: 120G (128849018880 bytes)
disk size: 11G
cluster_size: 65536
Snapshot list:
ID        TAG                 VM SIZE                DATE       VM CLOCK
1         1. Fresh installation      0 2016-04-21 23:02:43   00:00:00.000
Format specific information:
    compat: 1.1
    lazy refcounts: true
    refcount bits: 16
    corrupt: false
----------------

* Qcow2 image after shrinking:

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$ qemu-img info rhel-7_shrinked.qcow2
image: rhel-7_shrinked.qcow2
file format: qcow2
virtual size: 120G (128849018880 bytes)
disk size: 1.1G
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: false
    refcount bits: 16
    corrupt: false
----------------

* Command used for shrinking:

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# qemu-img convert -f qcow2 -O qcow2 rhel-7.qcow2 rhel-7_shrinked.qcow2
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