Re: General use of zstd instead of zlib compression
On Fri, Mar 14, 2025 at 03:34:46PM +0100, Peter Krempa wrote:
On Fri, Mar 14, 2025 at 14:18:03 -0000, Michael Niehren wrote:
> one more ...
>
> what would happen, if i create the qcow2 image with zstd compression enabled and
> use the '--reuse-external' flag ?
> Would qemu write compressed data in it or not ?
It would not be compressed, as I've explained earlier (On technical
lists it's preferred if context from what you're replying to is not
trimmed so that it can be reffred back to) actual compression of blocks
needs to be requested explicitly. The qcow2 header setting merely states
which algorithm should be used if blocks are compressed.
Also, AFAIK, qemu will not write compressed data during "normal" usage
by a running VM. The compression only gets applied during full image
conversion processes. iow, 'qemu-img convert' can be used to create a
compressed image, from a non-compressed image.
With regards,
Daniel
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