Comment 20 for bug 1025244

@Mario, in theory an image "that should be taking up 30 GB" with four snapshots should be taking up at most about 150 GB, of course. Now the question is what you mean by "should be taking up 30 GB" and by "is taking 600+ GB".

For the latter, did you query the file length (ls -l) or the actual size (qemu-img info, "disk size")?

For the former, if you have a virtual disk size of 1 TB and the guest reports 30 GB are used, that doesn't mean that qemu knows that only 30 GB are used. If you delete a file in the guest, it will report less space being used; however, qemu doesn't know about that unless the guest bothers to discard the now unused sectors. If it doesn't (and I don't see a reason why a guest should discard sectors on an HDD), the guest will just remove the file metadata but the data will stay there (and may be overwritten later by the guest when creating new files etc.). qemu has no idea that that data is now unused, therefore it must treat those sectors as being in use.

If your image indeed has a virtual disk size of 30 GB, has four snapshots, is clean (qemu-img check) and does take up 600+ GB of actual disk space, that should indeed not be happening (unless there's some case I forgot to consider).