Comment 15 for bug 1174153

We've had to deal with this problem before in Nova with the libvirt driver with its LVM volume backend.

In that case we will wipe the data at VM teardown, to ensure future VMs don't see any data from previous tenants

commit 9d2ea970422591f8cdc394001be9a2deca499a5f
Author: Pádraig Brady <email address hidden>
Date: Fri Nov 23 14:59:13 2012 +0000

    Don't leak info from libvirt LVM backed instances

    * nova/virt/libvirt/utils.py (remove_logical_volumes):
    Overwrite each logical volume with zero
    (clear_logical_volume): LV obfuscation implementation.
    (logical_volume_size): A utility function used by
    clear_logical_volume()

    Fixes bug: 1070539
    Change-Id: I4e1024de8dfe9b0be3b0d6437c836d2042862f85

We made this behaviour configurable with a nova.conf setting

commit 71946855591a41dcc87ef59656a8a340774eeaf2
Author: Pádraig Brady <email address hidden>
Date: Tue Feb 11 11:51:39 2014 +0000

    libvirt: support configurable wipe methods for LVM backed instances

    Provide configurable methods to clear these volumes.
    The new 'volume_clear' and 'volume_clear_size' options
    are the same as currently supported by cinder.

    * nova/virt/libvirt/imagebackend.py: Define the new options.
    * nova/virt/libvirt/utils.py (clear_logical_volume): Support the
    new options. Refactor the existing dd method out to
    _zero_logic_volume().
    * nova/tests/virt/libvirt/test_libvirt_utils.py: Add missing test cases
    for the existing clear_logical_volume code, and for the new code
    supporting the new clearing methods.
    * etc/nova/nova.conf.sample: Add the 2 new config descriptions
    to the [libvirt] section.

    Change-Id: I5551197f9ec89ae2f9b051696bccdeb1af2c031f
    Closes-Bug: #889299

IMHO we should move this config setting & code out of the libvirt section into the general nova.conf section and re-use the logic for baremetal.