On Tue, Nov 7, 2023 at 6:53 PM Alberto Garcia <be...@igalia.com> wrote:
> On Tue, Nov 07, 2023 at 05:32:22PM +0800, Han Han wrote: > > >>> Before blockcopy, check source image:🔄 ❓ > > >>> > > >> # qemu-img info -U > > >>> /var/lib/avocado/data/avocado-vt/images/jeos-27-x86_64.qcow2🔄 ❓ > > >>> > > >> > > > Was this a compressed qcow2 image when you started? maybe you started > with > > > an appliance image? > > > > > Hi, Nir, I have a question here: How to check if a qcow2 image is > > compressed? > > $ qemu-img map /path/to/image.qcow2 > > If it says "File contains external, encrypted or compressed clusters" > and the image is not encrypted then that's probably it. > > > The qcow2 file /var/lib/avocado/data/avocado-vt/images/copy.qcow2 is > > created without compress options, while the qemu-img info for it > > shows `compression type: zlib`. Is that mean the image is compressed > > as well? > > No, in qcow2 there is actually no such thing as a compressed image as > opposed to an uncompressed image. > > qcow2 images contain a collection of data clusters, and each > individual cluster can be either compressed or uncompressed. > > That zlib that qemu-img reports is the algorithm that is used for > compressed clusters *IF* they exist, but it's perfectly possible that > an image does not have any compressed cluster. > > Thanks for your detailed explanation. > Berto > >
