ctdb-docs: Document that tunables should be set the same on all nodes

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>

diff --git a/ctdb/doc/ctdb-tunables.7.xml b/ctdb/doc/ctdb-tunables.7.xml
index 8143a45a795e2bc5cc2af0bba6a7c1b670aaf381..1e263dac9a412782112f2edb694e6e2719d58b4b 100644 (file)
--- a/ctdb/doc/ctdb-tunables.7.xml
+++ b/ctdb/doc/ctdb-tunables.7.xml
@@ -29,6 +29,14 @@
       <command>getvar</command> commands for more details.
     </para>
 
+    <para>
+      Unless otherwise stated, tunables should be set to the same
+      value on all nodes.  Setting tunables to different values across
+      nodes may produce unexpected results.  Future releases may set
+      (some or most) tunables globally across the cluster but doing so
+      is currently a manual process.
+    </para>
+
     <para>
       The tunable variables are listed alphabetically.
     </para>
@@ -177,13 +185,12 @@
       <title>EnableBans</title>
       <para>Default: 1</para>
       <para>
-        This parameter allows ctdb to ban a node if the node is misbehaving.
+       This parameter allows ctdb to ban a node if the node is misbehaving.
       </para>
       <para>
        When set to 0, this disables banning completely in the cluster
        and thus nodes can not get banned, even it they break. Don't
-       set to 0 unless you know what you are doing.  You should set
-       this to the same value on all nodes to avoid unexpected behaviour.
+       set to 0 unless you know what you are doing.
       </para>
     </refsect2>
 
@@ -362,10 +369,9 @@
        If no nodes are HEALTHY then by default ctdb will happily host
        public IPs on disabled (unhealthy or administratively disabled)
        nodes.  This can cause problems, for example if the underlying
-       cluster filesystem is not mounted.  When set to 1 on a node and
-       that node is disabled, any IPs hosted by this node will be
-       released and the node will not takeover any IPs until it is no
-       longer disabled.
+       cluster filesystem is not mounted.  When set to 1 and a node
+       is disabled, any IPs hosted by this node will be released and
+       the node will not takeover any IPs until it is no longer disabled.
       </para>
     </refsect2>
 
@@ -374,9 +380,11 @@
       <para>Default: 0</para>
       <para>
        When set to 1, ctdb will not allow IP addresses to be failed
-       over onto this node. Any IP addresses that the node currently
-       hosts will remain on the node but no new IP addresses can be
-       failed over to the node.
+       over to other nodes.  Any IP addresses already hosted on
+       healthy nodes will remain.  Usually IP addresses hosted on
+       unhealthy nodes will also remain, if NoIPHostOnAllDisabled is
+       0.  However, if NoIPHostOnAllDisabled is 1 then IP addresses
+       will be released by unhealthy nodes and will become un-hosted.
       </para>
     </refsect2>