ceph-volume: fix fast device alloc size on mulitple device

The size computed by get_physical_fast_allocs() was wrong when the
function had multiple devices to treat.

For instance if there is 4 OSDs and 2 fast devices of each 10G while
allocating 2 slots per fast devvices. The behavior before was that each
slot would be 2.5G meaning that both fast devices would half full. The
behavior now is that each slot will take 5G so that the fast devices
would be full.

Fixes: https://tracker.ceph.com/issues/56031
Signed-off-by: Arthur Outhenin-Chalandre <arthur.outhenin-chalandre@cern.ch>
(cherry picked from commit d0f9e93)

src/ceph-volume/ceph_volume/devices/lvm/batch.py

@@ -119,14 +119,10 @@ def get_physical_fast_allocs(devices, type_, fast_slots_per_device, new_osds, ar
                 continue
             # any LV present is considered a taken slot
             occupied_slots = len(dev.lvs)
-            # prior to v15.2.8, db/wal deployments were grouping multiple fast devices into single VGs - we need to
-            # multiply requested_slots (per device) by the number of devices in the VG in order to ensure that
-            # abs_size is calculated correctly from vg_size
-            slots_for_vg = len(vg_devices) * requested_slots
             dev_size = dev.vg_size[0]
             # this only looks at the first vg on device, unsure if there is a better
             # way
-            abs_size = disk.Size(b=int(dev_size / slots_for_vg))
+            abs_size = disk.Size(b=int(dev_size / requested_slots))
             free_size = dev.vg_free[0]
             relative_size = int(abs_size) / dev_size
             if requested_size:

src/ceph-volume/ceph_volume/tests/conftest.py

@@ -58,9 +58,7 @@ def mock_lv():
         return dev
     return mock_lv
 
-
-@pytest.fixture
-def mock_devices_available():
+def mock_device():
     dev = create_autospec(device.Device)
     dev.path = '/dev/foo'
     dev.vg_name = 'vg_foo'
@@ -69,21 +67,18 @@ def mock_devices_available():
     dev.available_lvm = True
     dev.vg_size = [21474836480]
     dev.vg_free = dev.vg_size
-    return [dev]
+    dev.lvs = []
+    return dev
+
+@pytest.fixture(params=range(1,3))
+def mock_devices_available(request):
+    ret = []
+    for _ in range(request.param):
+        ret.append(mock_device())
+    return ret
 
 @pytest.fixture
 def mock_device_generator():
-    def mock_device():
-        dev = create_autospec(device.Device)
-        dev.path = '/dev/foo'
-        dev.vg_name = 'vg_foo'
-        dev.lv_name = 'lv_foo'
-        dev.vgs = [lvm.VolumeGroup(vg_name=dev.vg_name, lv_name=dev.lv_name)]
-        dev.available_lvm = True
-        dev.vg_size = [21474836480]
-        dev.vg_free = dev.vg_size
-        dev.lvs = []
-        return dev
     return mock_device
 
 

src/ceph-volume/ceph_volume/tests/devices/lvm/test_batch.py

@@ -216,6 +216,16 @@ def test_get_physical_fast_allocs_length(self, factory,
                                               'block_db', 2, 2, args)
         assert len(fast) == 2
 
+    def test_get_physical_fast_allocs_abs_size(self, factory,
+                                               conf_ceph_stub,
+                                               mock_devices_available):
+        conf_ceph_stub('[global]\nfsid=asdf-lkjh')
+        args = factory(block_db_slots=None, get_block_db_size=None)
+        fasts = batch.get_physical_fast_allocs(mock_devices_available,
+                                              'block_db', 2, 2, args)
+        for fast, dev in zip(fasts, mock_devices_available):
+            assert fast[2] == int(dev.vg_size[0] / 2)
+
     def test_batch_fast_allocations_one_block_db_length(self, factory, conf_ceph_stub,
                                                   mock_lv_device_generator):
         conf_ceph_stub('[global]\nfsid=asdf-lkjh')