Okay now that I actually look into this and wrap my head around it, virt-manager should change. See this previously mentioned change: https://github.com/virt-manager/virt-manager/commit/15a6a7e2105440df528f75c4df4d2471df28bd1e
The idea behind virt-manager's default was if user selected 'raw' for disk images, assume the user wants to maximize performance, so fully allocate the disk. qcow2 didn't support anything except sparse, so the sparse=True vs sparse=False made no difference. So we always set sparse=False Then qcow2 grows non-sparse support, and virt-manager is suddenly defaulting to it. That's a pretty big semantic change. Even if falloc is fast enough in most cases, it is still claiming all the storage up front. Which is not the historically intended behavior. So I pushed a change to virt-manager to default to only use non-sparse for raw format by default. That should side step this issue I'll be pushing a new release with the fix sometime this coming week commit ba08f84b3408744e9aa9763d100e8aa217c1f5ff Author: Cole Robinson <crobi...@redhat.com> Date: Sat Sep 19 18:06:45 2020 -0400 addstorage: Return to using qcow2 sparse by default -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1847105 Title: very slow disk creation, snapshotting To manage notifications about this bug go to: https://bugs.launchpad.net/virt-manager/+bug/1847105/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs