On Mon, Mar 16, 2020 at 17:25:50 +0800, Jing-Wei Su wrote: You can nowadays use blockcopy without undefine if you use the --transient-job flag. (If the VM crashes though the job can't be recovered and must be fully restarted). We could not continue the job. As you've pointed out it can be done now but it's not implemented. Either declare that you don't care about the job being irrecoverable if it fails or you'll need to wait until it's implemented. Unfortunately it's pretty low on my priority list right now.