Comment 46 for bug 1847105

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 <email address hidden>
Date: Sat Sep 19 18:06:45 2020 -0400

    addstorage: Return to using qcow2 sparse by default