doc/start: KRBD feature flag support note

Add KRBD feature flag support note to doc/start/os-recommendations.rst.

This change was suggested by Anthony D'Atri in https://github.com/ceph/ceph/pull/51485.

Co-authored-by: Ilya Dryomov <idryomov@redhat.com>
Co-authored-by: Anthony D'Atri <anthony.datri@gmail.com>
Signed-off-by: Zac Dover <zac.dover@proton.me>
(cherry picked from commit 2a619dba2d22749e6facaf8dd0d370e16a1672c4)

diff --git a/doc/start/os-recommendations.rst b/doc/start/os-recommendations.rst
index 64887c925c43f4f03f0ed460cd349f853a63e6bd..7b3671208e232114f37c25c198e8ea91e5a672e3 100644 (file)
--- a/doc/start/os-recommendations.rst
+++ b/doc/start/os-recommendations.rst
@@ -29,8 +29,10 @@ Linux Kernel
   for kernel version guidance.
 
   Older kernel client versions may not support your `CRUSH tunables`_ profile
-  or other newer features of the Ceph cluster, requiring the storage cluster
-  to be configured with those features disabled.
+  or other newer features of the Ceph cluster, requiring the storage cluster to
+  be configured with those features disabled. For RBD, a kernel of version 5.3
+  or CentOS 8.2 is the minimum necessary for reasonable support for RBD image
+  features.
 
 
 Platforms