In oVirt 4.1, the Enable Discard feature was introduced. This was found to be unreliable in combination with Wipe After Delete (WAD), in that a VM Disk with both flags configured could be removed from a VM and not have all of its blocks wiped. If the same storage pages were then assigned to another Virtual Machine, potentially sensitive data could be read from those pages instead of zeroes.
Acknowledgments: Name: Idan Shaby (Red Hat)
External References: https://gerrit.ovirt.org/#/c/84875 https://gerrit.ovirt.org/#/c/84861