|Subject:||Re: [Qemu-discuss] Info about compressed images|
|Date:||Wed, 25 Jan 2017 10:33:32 +0100|
On Fri, Jan 13, 2017 at 06:57:53PM +0100, Gianni Costanzi wrote:
> I'm new here and I've started using QEMU when I've started playing
> with Unetlab/EVE Network simulator.
> I have some questions about compression and images with a compressed
> backing file:
I think there's some misunderstanding here about compressed images in
QEMU. I'll try to clarify:
* You create a compressed image with 'qemu-img convert -c'. That is a
copy of the original image with all the clusters compressed.
* The compression is read-only: QEMU will read the compressed clusters,
but everything that it writes will be uncompressed (also if you
rewrite compressed clusters).
* Therefore, there's no such thing as an image with compression
enabled. In QEMU you don't compress an image, you compress
individual clusters of data. An image can have a mix of compressed
and uncompressed clusters.
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