On 30 Nov 2021, at 15:27, Daniel P. Berrangé <berrange@xxxxxxxxxx> wrote: > > On Tue, Nov 30, 2021 at 02:51:22PM +0100, Richard Taubo wrote: >> Hi! >> >> When running this command on Fedora 35 I get: >> [#] qemu-img create -o preallocation=full -f qcow2 /var/vm_mail/mytest.qcow2 10GB >> => Formatting '/var/vm_mail//mytest.qcow2', fmt=qcow2 . . . preallocation=full compression_type=zlib . . . ." >> >> Question: >> When using 'preallocation=full’ I was surprised that the resulting qcow2 image includes the 'compression_type=zlib’ part. >> Why/when is this compression used when the qcow2 image is fully preallocated? > > It doesn't mean the image is currently compressed. > > Rather it just records the desired compression algorithm for this image, > if any future writes were to be told to use compression. Okay, good to know. Thanks a lot! :-) Best regards Richard Taubo
