diff --git a/nova/tests/functional/regressions/test_bug_1550919.py b/nova/tests/functional/regressions/test_bug_1550919.py
new file mode 100644
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+++ b/nova/tests/functional/regressions/test_bug_1550919.py
@@ -0,0 +1,319 @@
+# Copyright 2018 Red Hat, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+import fixtures
+import mock
+import os.path
+
+from oslo_utils import fileutils
+from oslo_utils import units
+
+from nova import conf
+from nova import test
+from nova.tests import fixtures as nova_fixtures
+from nova.tests.functional import integrated_helpers
+from nova.tests.unit import fake_network
+from nova.tests.unit import fake_notifier
+import nova.tests.unit.image.fake as fake_image
+from nova.tests.unit.virt.libvirt import fakelibvirt
+
+CONF = conf.CONF
+
+
+class _FakeFlat(object):
+    def setUp(self):
+        super(_FakeFlat, self).setUp()
+
+        def fake_create_image(_self, prepare_template, base, size,
+                              *args, **kwargs):
+            # Simply ensure the file exists
+            open(_self.path, 'a').close()
+
+        self.useFixture(fixtures.MonkeyPatch(
+            'nova.virt.libvirt.imagebackend.Flat.create_image',
+            fake_create_image))
+
+
+class _FlatTest(_FakeFlat):
+    def setUp(self):
+        super(_FlatTest, self).setUp()
+
+        self.flags(group='libvirt', images_type='flat')
+
+    def assert_disks_nonshared_instancedir(self, server):
+        source_root_disk = os.path.join(self.source_instance_path(server),
+                                        'disk')
+        dest_root_disk = os.path.join(self.dest_instance_path(server),
+                                      'disk')
+
+        self.assertTrue(os.path.exists(source_root_disk),
+                        "Source root disk %s does not exist" %
+                        source_root_disk)
+        self.assertFalse(os.path.exists(dest_root_disk),
+                         "Destination root disk %s exists" % dest_root_disk)
+
+    def assert_disks_shared_instancedir(self, server):
+        source_root_disk = os.path.join(self.source_instance_path(server),
+                                        'disk')
+
+        # FIXME(mdbooth): We should not have deleted a shared root disk
+        self.assertFalse(os.path.exists(source_root_disk),
+                         "Source root disk %s exists" % source_root_disk)
+
+
+# NOTE(mdbooth): The Rbd tests also need to mock the flat backend, because the
+# image returned by the fake image service may (non-deterministically before
+# python3.6 due to dict ordering) include a kernel and ramdisk. The libvirt
+# driver forces these to use the flat backend.
+class _RbdTest(_FakeFlat):
+    def setUp(self):
+        super(_RbdTest, self).setUp()
+
+        self.flags(group='libvirt', images_type='rbd')
+
+        self.created = set()
+
+        def fake_create_image(_self, prepare_template, base, size,
+                              *args, **kwargs):
+            self.created.add(_self.rbd_name)
+
+        def fake_exists(_self):
+            return _self.rbd_name in self.created
+
+        self.useFixture(fixtures.MonkeyPatch(
+            'nova.virt.libvirt.imagebackend.Rbd.create_image',
+            fake_create_image))
+        self.useFixture(fixtures.MonkeyPatch(
+            'nova.virt.libvirt.imagebackend.Rbd.exists',
+            fake_exists))
+
+        # We never want to actually touch rbd
+        self.mock_rbd_driver = self.useFixture(fixtures.MockPatch(
+            'nova.virt.libvirt.storage.rbd_utils.RBDDriver')).mock.return_value
+        self.mock_rbd_driver.get_mon_addrs.return_value = ([], [])
+        self.mock_rbd_driver.size.return_value = 10 * units.Gi
+
+        self.mock_cleanup_rbd = self.useFixture(fixtures.MockPatch(
+            'nova.virt.libvirt.driver.LibvirtDriver._cleanup_rbd')).mock
+
+    def _assert_disks(self, server):
+        # Check that we created a root disk and haven't called _cleanup_rbd at
+        # all
+        self.assertIn("%s_disk" % server['id'], self.created)
+        # FIXME(mdbooth): we should not have deleted shared disks
+        self.assertEqual(1, self.mock_cleanup_rbd.call_count)
+
+    # We never want to cleanup rbd disks during evacuate, regardless of
+    # instance shared storage
+    assert_disks_nonshared_instancedir = _assert_disks
+    assert_disks_shared_instancedir = _assert_disks
+
+
+class _LibvirtEvacuateTest(integrated_helpers.InstanceHelperMixin):
+    def _start_compute(self, name):
+        # NOTE(mdbooth): fakelibvirt's getHostname currently returns a
+        # hardcoded 'compute1', which is undesirable if we want multiple fake
+        # computes. There's no good way to pre-initialise get_connection() to
+        # return a fake libvirt with a custom return for getHostname.
+        #
+        # Here we mock the class during service creation to return our custom
+        # hostname, but we can't leave this in place because then both computes
+        # will still get the same value from their libvirt Connection. Once the
+        # service has started, we poke a custom getHostname into the
+        # instantiated object to do the same thing, but only for that object.
+
+        with mock.patch.object(fakelibvirt.Connection, 'getHostname',
+                               return_value=name):
+            compute = self.start_service('compute', host=name)
+
+        compute.driver._host.get_connection().getHostname = lambda: name
+        return compute
+
+    def setUp(self):
+        super(_LibvirtEvacuateTest, self).setUp()
+
+        self.useFixture(nova_fixtures.NeutronFixture(self))
+        fake_network.set_stub_network_methods(self)
+        self.useFixture(nova_fixtures.PlacementFixture())
+
+        api_fixture = self.useFixture(
+                nova_fixtures.OSAPIFixture(api_version='v2.1'))
+
+        self.api = api_fixture.admin_api
+        # force_down and evacuate without onSharedStorage
+        self.api.microversion = '2.14'
+
+        fake_image.stub_out_image_service(self)
+        self.addCleanup(fake_image.FakeImageService_reset)
+
+        fake_notifier.stub_notifier(self)
+        self.addCleanup(fake_notifier.reset)
+
+        self.useFixture(fakelibvirt.FakeLibvirtFixture())
+
+        self.start_service('conductor')
+        self.start_service('scheduler')
+
+        self.flags(compute_driver='libvirt.LibvirtDriver')
+        self.compute0 = self._start_compute('compute0')
+
+        # Choice of image id and flavor are arbitrary. Fixed for consistency.
+        self.image_id = fake_image.AUTO_DISK_CONFIG_ENABLED_IMAGE_UUID
+        self.flavor_id = next(flavor for flavor in self.api.get_flavors()
+                              if flavor['name'] == 'm1.tiny')['id']
+
+    @staticmethod
+    def source_instance_path(server):
+        return os.path.join(CONF.instances_path, server['id'])
+
+    @staticmethod
+    def dest_instance_path(server):
+        return os.path.join(CONF.instances_path, 'dest', server['id'])
+
+    def _create_server(self):
+        create_req = {
+            'name': 'server',
+            'imageRef': self.image_id,
+            'flavorRef': self.flavor_id,
+        }
+        server = self.api.post_server({'server': create_req})
+        self.addCleanup(self.api.delete_server, server['id'])
+
+        self._wait_for_state_change(self.api, server, 'ACTIVE')
+
+        return server
+
+    def _swap_computes(self):
+        # Force compute0 down
+        self.compute0.stop()
+        self.api.force_down_service('compute0', 'nova-compute', True)
+
+        # Start compute1
+        self.compute1 = self._start_compute('compute1')
+
+        # Create a 'pass-through' mock for ensure_tree so we can log its calls
+        orig_ensure_tree = fileutils.ensure_tree
+        self.mock_ensure_tree = self.useFixture(fixtures.MockPatch(
+            'oslo_utils.fileutils.ensure_tree',
+            side_effect=orig_ensure_tree)).mock
+
+    def _evacuate_with_failure(self, server):
+        # Perform an evacuation during which we experience a failure on the
+        # destination host
+        instance_uuid = server['id']
+
+        with mock.patch.object(self.compute1.driver, 'plug_vifs') as plug_vifs:
+            plug_vifs.side_effect = test.TestingException
+
+            self.api.post_server_action(instance_uuid,
+                                        {'evacuate': {'host': 'compute1'}})
+
+            # Wait for the rebuild to start, then complete
+            fake_notifier.wait_for_versioned_notifications(
+                    'instance.rebuild.start')
+            self._wait_for_server_parameter(self.api, server,
+                                            {'OS-EXT-STS:task_state': None})
+
+            # Meta-test
+            plug_vifs.assert_called()
+
+        # Return fresh server state after evacuate
+        return self.api.get_server(instance_uuid)
+
+    def test_evacuate_nonshared_instancedir(self):
+        # If we fail during evacuate and the instance directory didn't
+        # previously exist on the destination, we should delete it
+
+        # Create an instance on compute0
+        server = self._create_server()
+        self._swap_computes()
+
+        source_instance_path = self.source_instance_path(server)
+        dest_instance_path = self.dest_instance_path(server)
+
+        # Check that we've got an instance directory on the source and not on
+        # the dest
+        self.assertTrue(os.path.exists(source_instance_path),
+                        "Source instance directory %s does not exist" %
+                        source_instance_path)
+        self.assertFalse(os.path.exists(dest_instance_path),
+                         "Destination instance directory %s exists" %
+                         dest_instance_path)
+
+        # By default our 2 compute hosts share the same instance directory on
+        # the test runner. Force a different directory while running evacuate
+        # on compute1 so we don't have shared storage.
+        def dest_get_instance_path(instance, relative=False):
+            if relative:
+                return instance.uuid
+            return dest_instance_path
+
+        with mock.patch('nova.virt.libvirt.utils.get_instance_path') \
+                as get_instance_path:
+            get_instance_path.side_effect = dest_get_instance_path
+            server = self._evacuate_with_failure(server)
+
+        # Check that we've got an instance directory on the source and not on
+        # the dest, but that the dest was created
+        self.assertTrue(os.path.exists(source_instance_path),
+                        "Source instance directory %s does not exist" %
+                        source_instance_path)
+        self.assertFalse(os.path.exists(dest_instance_path),
+                         "Destination instance directory %s exists" %
+                         dest_instance_path)
+        self.mock_ensure_tree.assert_called_with(dest_instance_path)
+
+        self.assert_disks_nonshared_instancedir(server)
+
+        # Check we're still on the failed source host
+        self.assertEqual('compute0', server['OS-EXT-SRV-ATTR:host'])
+
+    def test_evacuate_shared_instancedir(self):
+        # If we fail during evacuate and the instance directory was already
+        # present on the destination, we should leave it there
+
+        # By default our 2 compute hosts share the same instance directory on
+        # the test runner.
+
+        # Create an instance on compute0
+        server = self._create_server()
+        self._swap_computes()
+
+        shared_instance_path = self.source_instance_path(server)
+
+        # Check that we've got an instance directory on the source
+        self.assertTrue(os.path.exists(shared_instance_path),
+                        "Shared instance directory %s does not exist" %
+                        shared_instance_path)
+
+        server = self._evacuate_with_failure(server)
+
+        # Check that the instance directory still exists
+        # FIXME(mdbooth): the shared instance directory should still exist
+        self.assertFalse(os.path.exists(shared_instance_path),
+                         "Shared instance directory %s exists" %
+                         shared_instance_path)
+
+        self.assert_disks_shared_instancedir(server)
+
+        # Check we're still on the failed source host
+        self.assertEqual('compute0', server['OS-EXT-SRV-ATTR:host'])
+
+
+class LibvirtFlatEvacuateTest(_LibvirtEvacuateTest, _FlatTest, test.TestCase):
+    pass
+
+
+class LibvirtRbdEvacuateTest(_LibvirtEvacuateTest, _RbdTest, test.TestCase):
+    pass