ceph: troubleshooting: revise and add frequently needed information

Existing information is slightly modified and retained.

Add information:
* List which logs are usually helpful for troubleshooting
* Explain how to acknowledge listed Ceph crashes and view details
* List common causes of Ceph problems and link to recommendations for a
  healthy cluster
* Briefly describe the common problem "OSDs down/crashed"

Signed-off-by: Alexander Zeidler <a.zeidler@proxmox.com>
[AL]: use old anchor to sub chapter that was kept to not break links
Signed-off-by: Aaron Lauterer <a.lauterer@proxmox.com>

pveceph.adoc

@@ -1150,22 +1150,78 @@ The following Ceph commands can be used to see if the cluster is healthy
 ('HEALTH_OK'), if there are warnings ('HEALTH_WARN'), or even errors
 ('HEALTH_ERR'). If the cluster is in an unhealthy state, the status commands
 below will also give you an overview of the current events and actions to take.
+To stop their execution, press CTRL-C.
 
 ----
-# single time output
+# Continuously watch the cluster status
-pve# ceph -s
+pve# watch ceph --status
-# continuously output status changes (press CTRL+C to stop)
+
-pve# ceph -w
+# Print the cluster status once (not being updated)
+# and continuously append lines of status events
+pve# ceph --watch
 ----
 
+[[pve_ceph_ts]]
+Troubleshooting
+~~~~~~~~~~~~~~~
+
+This section includes frequently used troubleshooting information.
+More information can be found on the official Ceph website under
+Troubleshooting
+footnote:[Ceph troubleshooting {cephdocs-url}/rados/troubleshooting/].
+
+[[pve_ceph_ts_logs]]
+.Relevant Logs on Affected Node
+
+* xref:disk_health_monitoring[Disk Health Monitoring]
+* __System -> System Log__ (or, for example,
+  `journalctl --since "2 days ago"`)
+* IPMI and RAID controller logs
+
+Ceph service crashes can be listed and viewed in detail by running
+`ceph crash ls` and `ceph crash info <crash_id>`. Crashes marked as
+new can be acknowledged by running, for example,
+`ceph crash archive-all`.
+
 To get a more detailed view, every Ceph service has a log file under
 `/var/log/ceph/`. If more detail is required, the log level can be
 adjusted footnote:[Ceph log and debugging {cephdocs-url}/rados/troubleshooting/log-and-debug/].
 
-You can find more information about troubleshooting
+[[pve_ceph_ts_causes]]
-footnote:[Ceph troubleshooting {cephdocs-url}/rados/troubleshooting/]
+.Common Causes of Ceph Problems
-a Ceph cluster on the official website.
 
+* Network problems like congestion, a faulty switch, a shut down
+interface or a blocking firewall. Check whether all {pve} nodes are
+reliably reachable on the
+xref:pvecm_cluster_network[corosync cluster network] and on the
+xref:pve_ceph_install_wizard[Ceph public and cluster network].
+
+* Disk or connection parts which are:
+** defective
+** not firmly mounted
+** lacking I/O performance under higher load (e.g. when using HDDs,
+consumer hardware or
+xref:pve_ceph_recommendation_raid[inadvisable RAID controllers])
+
+* Not fulfilling the xref:_recommendations_for_a_healthy_ceph_cluster[recommendations] for
+a healthy Ceph cluster.
+
+[[pve_ceph_ts_problems]]
+.Common Ceph Problems
+ ::
+
+OSDs `down`/crashed:::
+A faulty OSD will be reported as `down` and mostly (auto) `out` 10
+minutes later. Depending on the cause, it can also automatically
+become `up` and `in` again. To try a manual activation via web
+interface, go to __Any node -> Ceph -> OSD__, select the OSD and click
+on **Start**, **In** and **Reload**. When using the shell, run on the
+affected node `ceph-volume lvm activate --all`.
++
+To activate a failed OSD, it may be necessary to
+xref:ha_manager_node_maintenance[safely reboot] the respective node
+or, as a last resort, to
+xref:pve_ceph_osd_replace[recreate or replace] the OSD.
 
 ifdef::manvolnum[]
 include::pve-copyright.adoc[]