From: Ilya Dryomov <idryomov@gmail.com>
Date: Thu, 6 May 2021 09:20:23 +0000 (+0200)
Subject: doc/rbd/rbd-persistent-write-back-cache: clarify some config settings
X-Git-Tag: v16.2.5~116^2
X-Git-Url: http://git-server-git.apps.pok.os.sepia.ceph.com/?a=commitdiff_plain;h=refs%2Fpull%2F41281%2Fhead;p=ceph.git

doc/rbd/rbd-persistent-write-back-cache: clarify some config settings

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
(cherry picked from commit 797709ebb18175fae2cff8b7f788019dd7c274a5)
---

diff --git a/doc/rbd/rbd-persistent-write-back-cache.rst b/doc/rbd/rbd-persistent-write-back-cache.rst
index 2ac146d5f2b5..db91e0697f16 100644
--- a/doc/rbd/rbd-persistent-write-back-cache.rst
+++ b/doc/rbd/rbd-persistent-write-back-cache.rst
@@ -47,8 +47,8 @@ need to be enabled.::
         rbd persistent cache mode = {cache-mode}
         rbd plugins = pwl_cache
 
-Value of {cache-mode} can be ``rwl`` or ``ssd``. By default it is
-``disabled``
+Value of {cache-mode} can be ``rwl``, ``ssd`` or ``disabled``. By default the
+cache is disabled.
 
 Here are some cache configuration settings:
 
@@ -56,10 +56,12 @@ Here are some cache configuration settings:
   have DAX enabled (see `DAX`_) when using ``rwl`` mode to avoid performance
   degradation.
 
-- ``rbd_persistent_cache_size`` The cache size per image.
+- ``rbd_persistent_cache_size`` The cache size per image. The minimum cache
+  size is 1 GB.
 
 - ``rbd_persistent_cache_log_periodic_stats`` This is a debug option. It is
-  used to emit periodic perf stats to the debug log.
+  used to emit periodic perf stats to the debug log if ``debug rbd pwl`` is
+  set to ``1`` or higher.
 
 The above configurations can be set per-host, per-pool, per-image etc. Eg, to
 set per-host, add the overrides to the appropriate `section`_ in the host's