Document the WAL/DB parameters for the 'disk add' action.

Signed-off-by: Luciano Lo Giudice <[email protected]>

docs/reference/commands/disk.rst

@@ -29,6 +29,40 @@ Global options:
    -v, --verbose     Show all information messages
        --version     Print version number
 
+``add``
+-------
+
+Adds a disk to the cluster, alongside optional devices for
+write-ahead logging and database management.
+
+Syntax:
+
+.. code-block:: none
+
+   microceph disk add <data-device> [options]
+
+Options:
+
+.. code-block:: none
+
+   --wipe          Wipe the data device.
+   --encrypt       Encrypt the data device.
+   --wal-device    Path to the block device used for write-ahead logging (WAL).
+   --wal-wipe      Wipe the WAL block device.
+   --wal-encrypt   Encrypt the WAL block device.
+   --db-device     Path to the block device to be used for database management.
+   --db-wipe       Wipe the DB block device.
+   --db-encrypt    Encrypt the DB block device.
+
+.. note::
+
+   Only the data device is mandatory. THe WAL and DB devices can improve
+   performance by delegating the management of some subsystems to additional
+   block devices. The WAL block device stores the internal journal whereas
+   the DB one stores metadata. Using either of those should be advantageous
+   as long as they are faster than the data device. WAL should take priority
+   over DB if there isn't enough storage for both.
+
 ``remove``
 ----------