diff --git a/driver.py b/driver.py
index 1ed6409..da284bb 100644
--- a/driver.py
+++ b/driver.py
@@ -90,6 +90,7 @@ from nova.virt.libvirt import imagebackend
 from nova.virt.libvirt import imagecache
 from nova.virt.libvirt import utils as libvirt_utils
 from nova.virt import netutils
+from nova.virt import images

 native_threading = patcher.original("threading")
 native_Queue = patcher.original("Queue")
@@ -852,7 +853,41 @@ class LibvirtDriver(driver.ComputeDriver):
                 # tree, this shouldn't block deletion of
                 # the instance as whole.
                 try:
+
+                    # pivotal story 684427
+                    file_backed_disk = target + '/disk'
+                    if os.path.exists(file_backed_disk):
+
+                        vol_size = int(images.qemu_img_info(file_backed_disk).virtual_size)
+                        bs = 1024 * 1024
+                        direct_flags = ('oflag=direct',)
+                        sync_flags = ()
+                        remaining_bytes = vol_size
+
+                        LOG.info(_('Writing %s bytes of zeros to file backed disk %s') % (vol_size, file_backed_disk))
+
+                        # The loop caters for versions of dd that
+                        # don't support the iflag=count_bytes option.
+                        while remaining_bytes:
+                            zero_blocks = remaining_bytes / bs
+                            seek_blocks = (vol_size - remaining_bytes) / bs
+                            zero_cmd = ('dd', 'bs=%s' % bs,
+                                        'if=/dev/zero', 'of=%s' % file_backed_disk,
+                                        'seek=%s' % seek_blocks, 'count=%s' % zero_blocks)
+                            zero_cmd += direct_flags
+                            zero_cmd += sync_flags
+                            if zero_blocks:
+                                utils.execute(*zero_cmd, run_as_root=True)
+                            remaining_bytes %= bs
+                            bs /= 1024  # Limit to 3 iterations
+                            # Use O_DIRECT with initial block size and fdatasync otherwise
+                            direct_flags = ()
+                            sync_flags = ('conv=fdatasync',)
+
+                    # now that we've overritten the file with 0s, we can
+                    # safely remove it
                     shutil.rmtree(target)
+
                 except OSError, e:
                     LOG.error(_("Failed to cleanup directory %(target)s: %(e)s"
                                 ) % locals())