docs: add docs for the lvm_osds OSD scenario

Signed-off-by: Andrew Schoen <aschoen@redhat.com>

docs/source/index.rst

@@ -18,6 +18,12 @@ Testing
 OSDs
 ====
 
+.. toctree::
+   :maxdepth: 1
+
+   osds/scenarios
+    
+
 MONs
 ====
 

docs/source/osds/scenarios.rst

@@ -0,0 +1,27 @@
+OSD Scenarios
+=============
+
+lvm_osds
+--------
+This OSD scenario uses ``ceph-volume`` to create OSDs from logical volumes and
+is only available when the ceph release is Luminous or greater.
+
+.. note::
+   The creation of the logical volumes is not supported by ceph-ansible, ceph-volume
+   only creates OSDs from existing logical volumes.
+
+Use ``lvm_osds:true`` to enable this scenario. Currently we only support dedicated journals
+when using lvm, not collocated journals.
+
+To configure this scenario use the ``lvm_volumes`` config option. ``lvm_volumes``  is a dictionary whose
+key/value pairs represent a data lv and a journal pair. Journals can be either a lv, device or partition.
+You can not use the same journal for many data lvs.
+
+For example, a configuration to use ``lvm_osds`` would look like::
+    
+    lvm_osds: true
+
+    lvm_volumes:
+      data-lv1: journal-lv1
+      data-lv2: /dev/sda
+      data:lv3: /dev/sdb1