Onapp has the same issue by default, it's not set by default to zero fill the old disks are being destroyed. This need to specifically be enabled in the config

Onapp has the same issue by default, it's not set by default to zero fill the old disks are being destroyed. This need to specifically be enabled in the config file by the administrators. In case you are running a VM on top of their platform you may want to check to make sure this is enabled.