JacksonChen666
commented
2 years ago a possible method that doesn't take up the space to shrink the image is with (ssd) trimming/discards, provided the drives has the options to shrink the image on discards (by default, it doesn't). this method depends on the OS to trim the free space, triggered manually or automatically.
i tested with utm by exporting the qemu command, removing the drive from the vm, copied the drive arguments from the exported command, recreated the image (because utm deletes the image without question, which isn't revert-able), and appended ,discard=unmap,detect-zeroes=unmap (source) to the end of the -drive argument.
wrote a file with random bytes, removed it, and triggered a trim on empty space. the empty space (which previously had data) was discarded, and the size of the image has reduced while the vm is still up.
the time to reduce the size is considerably significant because it doesn't spend time rewriting the entire used space.
here is just an example i did (video, 411 kB)
(editing existing auto-generated qemu arguments isn't a feature and i'd really like that (still advanced but useful in some cases))
for making it smaller by converting with qemu-img, expand my previous comment below for my concerns of such.
conath
brunocastello
osy
ktprograms
adespoton
rotu
I posted the following on this discussion and @conath suggested me to add it as a feature request:
VMware provides this as a way to reclaim disk space: https://www.askdavetaylor.com/vmware-fusion-is-eating-up-my-hard-drive-help/
UTM could do a similar thing with qemu-img and qcow2 images. Say you have a machine and specified it to have a max 64GB. And you are currently using 34GB of 64GB. Now, what if you install a program (like an Adobe Creative Cloud suite, for example) and it eats up more 6GB, adding up to 40GB of usage, but you regret it and uninstall the whole suite, but you are left with a 40GB qcow2 image instead of 34GB, and unused 6GB? You might want that space back.
VMware deals with it by adding a "Clean Up Virtual Machine" which reclaims the unused 6GB disk space.
I usually deal with it using a command line with qemu-img:
qemu-img convert -O qcow2 win11.qcow2 win11_small.qcow2then I deletewin11.qcow2, and finally I rename thewin11_small.qcow2towin11.qcow2This process does shrink the image from 40GB to 34GB (or maybe even more, depending of your mileage and disk usage).
Basically you would need to do some kind of script to automatize this process and add a button to the machine configuration to do that, just like how VMware does. The process does take some considerable time to finish (depending of your machine image size), so you might need to add a pop-up screen asking the user to wait until the process is finished (VMware does the same for its Linux machines).