[PATCH pve-docs 1/1] pvecm: config: document how to change the token coefficient

[Friedrich Weber <f.weber@proxmox.com>]

New clusters are created with a lower coefficient. Users with existing
clusters or users who prefer a different token coefficient may want to
change the token coefficient. Hence, add a note how to change the
token coefficient to the admin guide.

Signed-off-by: Friedrich Weber <f.weber@proxmox.com>
---

Notes:
    - should this already include more details (in which cases changing
      the coefficient may be necessary?) in this first version?
    
    - currently, changing the token_coefficient in /etc/pve/corosync.conf
      without a corosync restart updates token and consensus timeouts, but
      knet_ping_timeout and knet_ping_interval are not updated, this is
      the reason why the patch suggests a corosync restart. I filed a bug
      for this [1] and there is a promising pull request [2] that appears
      to fix the issue. So the question is whether we want to backport [2]
      (when it's merged), and if yes, whether we want to remove the
      restart suggestion from the docs.
    
    [1] https://github.com/corosync/corosync/issues/813
    [2] https://github.com/corosync/corosync/pull/814

 pvecm.adoc | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/pvecm.adoc b/pvecm.adoc
index 0ed1bd2..9513a6c 100644
--- a/pvecm.adoc
+++ b/pvecm.adoc
@@ -1371,6 +1371,23 @@ systemctl restart corosync
 
 On errors, check the troubleshooting section below.
 
+Changing the token cofficient
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The token coefficient can be configured in the `totem` section in
+`/etc/pve/corosync.conf`. corosync uses the token coefficient to calculate
+several timeouts in relation to the cluster size.footnote:[
+`token_coefficient` in the corosync manual page
+https://manpages.debian.org/stable/corosync/corosync.conf.5.en.html#token_coefficient]
+
+If the token coefficient is not explicitly set, it defaults to 650 milliseconds.
+New clusters are created with a lower token coefficient of 125ms that is
+explicitly set in `/etc/pve/corosync.conf`.
+
+You can change the token coefficient of an existing cluster by
+xref:pvecm_edit_corosync_conf[editing corosync.conf]. For the change to fully
+take effect, you need to restart corosync on all nodes.
+
 Troubleshooting
 ~~~~~~~~~~~~~~~
 
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