doc/ceph-volume lvm prepare can accept devices for --data

Signed-off-by: Alfredo Deza <adeza@redhat.com>
(cherry picked from commit 9bfab348b2ff59c0b939a19c22d4a06bc5236b96)

Conflicts:
	doc/ceph-volume/lvm/prepare.rst

diff --git a/doc/ceph-volume/lvm/prepare.rst b/doc/ceph-volume/lvm/prepare.rst
index dfb49c54efea35b63b00405045bdc51734d8487a..27ebb55d7e6283c0549c9c2af5f41edee28e8221 100644 (file)
--- a/doc/ceph-volume/lvm/prepare.rst
+++ b/doc/ceph-volume/lvm/prepare.rst
@@ -33,17 +33,37 @@ the back end can be specified with:
 This is the OSD backend that allows preparation of logical volumes for
 a :term:`filestore` objectstore OSD.
 
-The process is *very* strict, it requires an existing logical volume for the
-OSD data and a partitioned physical device or logical volume for the journal.
-No special preparation is needed for these volumes other than following the
-minimum size requirements for data and journal.
+It can use a logical volume for the OSD data and a partitioned physical device
+or logical volume for the journal.  No special preparation is needed for these
+volumes other than following the minimum size requirements for data and
+journal.
 
 The API call looks like::
 
     ceph-volume prepare --filestore --data data --journal journal
 
-The journal *must* be a logical volume, just like the data volume, and that
-argument is always required even if both live under the same group.
+There is flexibility to use a raw device or partition as well for ``--data``
+that will be converted to a logical volume. This is not ideal in all situations
+since ``ceph-volume`` is just going to create a unique volume group and
+a logical volume from that device.
+
+When using logical volumes for ``--data``, the  value *must* be a volume group
+name and a logical volume name separated by a ``/``. Since logical volume names
+are not enforced for uniqueness, this prevents using the wrong volume. The
+``--journal`` can be either a logical volume *or* a partition.
+
+When using a partition, it *must* contain a ``PARTUUID`` discoverable by
+``blkid``, so that it can later be identified correctly regardless of the
+device name (or path).
+
+When using a partition, this is how it would look for ``/dev/sdc1``::
+
+    ceph-volume prepare --filestore --data volume_group/lv_name --journal /dev/sdc1
+
+For a logical volume, just like for ``--data``, a volume group and logical
+volume name are required::
+
+    ceph-volume prepare --filestore --data volume_group/lv_name --journal volume_group/journal_lv
 
 A generated uuid is used to ask the cluster for a new OSD. These two pieces are
 crucial for identifying an OSD and will later be used throughout the
@@ -115,11 +135,10 @@ more flexibility for devices. Bluestore supports the following configurations:
 * A block device and a block.db device
 * A single block device
 
-It can accept a whole device (not a partition, otherwise it will raise an
-error) or a logical volume for ``block``. If a physical device is provided it
-will then be turned into a logical volume. This allows a simpler approach at
-using LVM but at the cost of flexibility: there are no options or
-configurations to change how the LV is created.
+It can accept a whole device (or partition), or a logical volume for ``block``.
+If a physical device is provided it will then be turned into a logical volume.
+This allows a simpler approach at using LVM but at the cost of flexibility:
+there are no options or configurations to change how the LV is created.
 
 The ``block`` is specified with the ``--data`` flag, and in its simplest use
 case it looks like::