doc:crimson-dev: add RANDOM_BLOCK_SSD usage example, fix indentation

Signed-off-by: Jose J Palacios-Perez <perezjos@uk.ibm.com>

diff --git a/doc/dev/crimson/index.rst b/doc/dev/crimson/index.rst
index 3f85159502f6f08edc45939b866c666b3bb9373f..fc7ec7fa3fff4e61056b3d64da4369135f484b59 100644 (file)
--- a/doc/dev/crimson/index.rst
+++ b/doc/dev/crimson/index.rst
@@ -40,13 +40,21 @@ The following options can be used with ``vstart.sh``.
 
 ``--osd-args``
     Pass extra command line options to ``crimson-osd`` or ``ceph-osd``.
-    This is useful for passing Seastar options to ``crimson-osd``. For
-    example, one can supply ``--osd-args "--memory 2G"`` to set the amount of
-    memory to use. Please refer to the output of::
+    This option is useful for passing either:
 
-      crimson-osd --help-seastar
+    #.  Seastar options, i.e., to indicate CPU core options, native backend options, etc.
+    #.  Object Store options, i.e. Seastore, to indicate the main backend device type.
+        For example, one can supply ``--osd-args "--memory 2G"`` to set the
+        amount of memory to use.
+
+.. note::
+    #. Please refer to `src/common/options/crimson.yaml.in` for valid `osd-args` options (in particular for Seastore).
+    #. Please refer to the output of::
+
+          crimson-osd --help-seastar
+
+       for additional Seastar-specific command line options.
 
-    for additional Seastar-specific command line options.
 
 ``--crimson-smp``
     The number of cores to use for each OSD.
@@ -85,6 +93,17 @@ To start a cluster with a single Crimson node, run::
     --without-dashboard --bluestore --crimson \
     --redirect-output
 
+
+To start a cluster with a single OSD using some Seastore options, in
+particular selecting the device type backend as Random Block Manager (RBM) for NVMe,
+run::
+
+  $ MDS=0 MON=1 OSD=1 MGR=1 taskset -ac '0-95' /ceph/src/vstart.sh --new -x \
+  --localhost --without-dashboard --redirect-output --seastore --osd-args \
+  "--seastore_max_concurrent_transactions=128 --seastore_cachepin_type=LRU \
+  --seastore_main_device_type=RANDOM_BLOCK_SSD" --seastore-devs  /dev/nvme0n1 \
+  --crimson  --crimson-smp 1 --no-restart
+
 Another SeaStore example::
 
   $  MGR=1 MON=1 OSD=1 MDS=0 RGW=0 ../src/vstart.sh -n -x \