Set default lvm_type to auto

We've had an lvm_type=thin for quite some time, and we've wanted to
make it Cinders default for a while, but there's no clean way to
migrate on upgrades.  So, we have a compromise, detect if the
deployment has volumes (including the thin pool).  If there are no
LVs or if the thin pool exists, use thin.  Otherwise, use the old
thick lvm-default.

This patch makes the default setting "auto" instead of "default"
(which is actually thick).

DocImpact: Need to update docs to reflect the default setting for
new deployments is auto (thin)

Change-Id: If25e814eb6282fef9a1dd30d17c80eab6860e275

cinder/tests/unit/volume/drivers/test_lvm_driver.py

@@ -98,11 +98,13 @@ def test_delete_volume_thinlvm_snap(self, _mock_create_export,
 
     @mock.patch.object(volutils, 'get_all_volume_groups',
                        return_value=[{'name': 'cinder-volumes'}])
-    def test_check_for_setup_error(self, vgs):
+    @mock.patch('cinder.brick.local_dev.lvm.LVM.get_lvm_version',
+                return_value=(2, 2, 100))
+    def test_check_for_setup_error(self, _mock_get_version, vgs):
         vg_obj = fake_lvm.FakeBrickLVM('cinder-volumes',
                                        False,
                                        None,
-                                       'default')
+                                       'auto')
 
         configuration = conf.Configuration(fake_opt, 'fake_group')
         lvm_driver = lvm.LVMVolumeDriver(configuration=configuration,

cinder/volume/drivers/lvm.py

@@ -51,7 +51,7 @@
                help='If >0, create LVs with multiple mirrors. Note that '
                     'this requires lvm_mirrors + 2 PVs with available space'),
     cfg.StrOpt('lvm_type',
-               default='default',
+               default='auto',
                choices=['default', 'thin', 'auto'],
                help='Type of LVM volumes to deploy; (default, thin, or auto). '
                     'Auto defaults to thin if thin is supported.'),

releasenotes/notes/lvm-type-default-to-auto-a2ad554fc8bb25f2.yaml

@@ -0,0 +1,7 @@
+---
+other:
+  - |
+    Modify default lvm_type setting from thick to auto.  This will result in
+    Cinder preferring thin on init, if there are no LV's in the VG it will
+    create a thin-pool and use thin.  If there are LV's and no thin-pool
+    it will continue using thick.